diff --git a/phpunit/code/constructor_visibility_inherited_private.php b/phpunit/code/constructor_visibility_inherited_private.php
new file mode 100644
index 00000000..53ace63a
--- /dev/null
+++ b/phpunit/code/constructor_visibility_inherited_private.php
@@ -0,0 +1,17 @@
+<?php
+
+class PrivateConstructorParent
+{
+    private function __construct()
+    {
+    }
+}
+
+class PrivateConstructorChild extends PrivateConstructorParent
+{
+}
+
+function main()
+{
+    new PrivateConstructorChild();
+}
diff --git a/phpunit/code/constructor_visibility_internal_private.php b/phpunit/code/constructor_visibility_internal_private.php
new file mode 100644
index 00000000..afe70b6e
--- /dev/null
+++ b/phpunit/code/constructor_visibility_internal_private.php
@@ -0,0 +1,6 @@
+<?php
+
+function main()
+{
+    new Closure();
+}
diff --git a/phpunit/code/constructor_visibility_namespaced.php b/phpunit/code/constructor_visibility_namespaced.php
new file mode 100644
index 00000000..cc4afb76
--- /dev/null
+++ b/phpunit/code/constructor_visibility_namespaced.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace ConstructorVisibility;
+
+class Hidden
+{
+    private function __construct()
+    {
+    }
+}
+
+function main()
+{
+    new Hidden();
+}
diff --git a/phpunit/code/constructor_visibility_private.php b/phpunit/code/constructor_visibility_private.php
new file mode 100644
index 00000000..89f7c1aa
--- /dev/null
+++ b/phpunit/code/constructor_visibility_private.php
@@ -0,0 +1,11 @@
+<?php
+
+class TestClass
+{
+    private function __construct(){}
+}
+
+function main()
+{
+    new TestClass;
+}
diff --git a/phpunit/code/constructor_visibility_protected.php b/phpunit/code/constructor_visibility_protected.php
new file mode 100644
index 00000000..64e31b55
--- /dev/null
+++ b/phpunit/code/constructor_visibility_protected.php
@@ -0,0 +1,11 @@
+<?php
+
+class TestClass
+{
+    protected function __construct(){}
+}
+
+function main()
+{
+    new TestClass;
+}
diff --git a/phpunit/code/constructor_visibility_protected_foreign_class.php b/phpunit/code/constructor_visibility_protected_foreign_class.php
new file mode 100644
index 00000000..d158987b
--- /dev/null
+++ b/phpunit/code/constructor_visibility_protected_foreign_class.php
@@ -0,0 +1,19 @@
+<?php
+
+class Base
+{
+    protected function __construct(){}
+}
+
+class Other
+{
+    public static function make(): Base
+    {
+        return new Base();
+    }
+}
+
+function main()
+{
+    Other::make();
+}
diff --git a/phpunit/code/trait_constructor_conflict.php b/phpunit/code/trait_constructor_conflict.php
new file mode 100644
index 00000000..695eee02
--- /dev/null
+++ b/phpunit/code/trait_constructor_conflict.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+trait TraitA
+{
+    public function __construct()
+    {
+        echo "A\n";
+    }
+}
+
+trait TraitB
+{
+    public function __construct()
+    {
+        echo "B\n";
+    }
+}
+
+class TestClass
+{
+    use TraitA, TraitB;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/code/trait_constructor_private.php b/phpunit/code/trait_constructor_private.php
new file mode 100644
index 00000000..2dc1db14
--- /dev/null
+++ b/phpunit/code/trait_constructor_private.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    private function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/code/trait_constructor_protected.php b/phpunit/code/trait_constructor_protected.php
new file mode 100644
index 00000000..be585075
--- /dev/null
+++ b/phpunit/code/trait_constructor_protected.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    protected function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
diff --git a/phpunit/src/ConstructorVisibilityTest.php b/phpunit/src/ConstructorVisibilityTest.php
new file mode 100644
index 00000000..fa0fd311
--- /dev/null
+++ b/phpunit/src/ConstructorVisibilityTest.php
@@ -0,0 +1,78 @@
+<?php
+
+use TypePhp\Exception\TestError;
+
+class ConstructorVisibilityTest extends BaseTest
+{
+    /**
+     * 编译期错误在转换阶段直接以 TestError 抛出，而在桩文件生成阶段
+     * (gen_stub.php) 会被包成 RuntimeException，这里两者都要捕获。
+     */
+    protected function exec(string $expected, string $file): void
+    {
+        try {
+            $this->compile($file);
+        } catch (TestError|RuntimeException $exception) {
+            $this->assertStringContainsString($expected, $exception->getMessage());
+            return;
+        }
+        $this->fail('Expected compile-time error was not thrown');
+    }
+
+    public function testPrivateConstructorCannotBeCalledFromOutside(): void
+    {
+        // 私有构造器不能从类外部通过 `new` 调用
+        $this->exec('Cannot call private TestClass::__construct()', 'constructor_visibility_private.php');
+    }
+
+    public function testProtectedConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // 保护构造器不能从全局作用域调用
+        $this->exec('Cannot call protected TestClass::__construct()', 'constructor_visibility_protected.php');
+    }
+
+    public function testProtectedConstructorCannotBeCalledFromNonSubclass(): void
+    {
+        // 保护构造器不能从非子类的其它类内部调用
+        $this->exec('Cannot call protected Base::__construct()', 'constructor_visibility_protected_foreign_class.php');
+    }
+
+    public function testInheritedPrivateConstructorCannotBeCalledFromChildScope(): void
+    {
+        $this->exec(
+            'Cannot call private PrivateConstructorParent::__construct()',
+            'constructor_visibility_inherited_private.php'
+        );
+    }
+
+    public function testInternalPrivateConstructorCannotBeCalled(): void
+    {
+        $this->exec('Cannot call private Closure::__construct()', 'constructor_visibility_internal_private.php');
+    }
+
+    public function testNamespacedConstructorUsesPhpClassNameInDiagnostic(): void
+    {
+        $this->exec(
+            'Cannot call private ConstructorVisibility\Hidden::__construct()',
+            'constructor_visibility_namespaced.php'
+        );
+    }
+
+    public function testTraitPrivateConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // trait 提供的私有构造器扁平化后等价于类的私有构造器
+        $this->exec('Cannot call private TestClass::__construct()', 'trait_constructor_private.php');
+    }
+
+    public function testTraitProtectedConstructorCannotBeCalledFromGlobalScope(): void
+    {
+        // trait 提供的保护构造器扁平化后等价于类的保护构造器
+        $this->exec('Cannot call protected TestClass::__construct()', 'trait_constructor_protected.php');
+    }
+
+    public function testConflictingTraitConstructorMustBeResolved(): void
+    {
+        // 两个 trait 各自声明 __construct 时必须显式解决冲突
+        $this->exec('Trait `TraitB` method `__construct` already exists', 'trait_constructor_conflict.php');
+    }
+}
diff --git a/src/CompilerBase.php b/src/CompilerBase.php
index c183b5a9..5a2f709a 100644
--- a/src/CompilerBase.php
+++ b/src/CompilerBase.php
@@ -3172,11 +3172,17 @@ class CompilerBase implements PropertyAccessContext
                         $className = $this->getNamespacedClassName($className);
                     }
                     $ctorClassName = $className;
-                    if ($this->hasClass($className)) {
-                        $classDef = $this->getClass($className);
-                        if ($classDef->flags & Modifiers::ABSTRACT) {
-                            $this->fatalError($expr, "abstract class `{$className}` cannot be instantiated");
-                        }
+                    if ($this->isAbstractClass($className)) {
+                        $this->fatalError($expr, "abstract class `{$className}` cannot be instantiated");
+                    }
+                    $constructor = $this->findConstructor($className);
+                    if ($constructor !== null
+                        && !$this->checkAccessibleByClassName($constructor['className'], $constructor['flags'])) {
+                        $this->fatalError(
+                            $expr,
+                            'Cannot call ' . $this->visibilityLabel($constructor['flags']) . ' '
+                            . $constructor['className'] . '::__construct()'
+                        );
                     }
                     $cePtr = $this->getClassEntryPtr($className);
                 }
@@ -3833,6 +3839,11 @@ class CompilerBase implements PropertyAccessContext
     }
 
     protected function checkAccessible(ClassDef $classDef, int $flags): bool
+    {
+        return $this->checkAccessibleByClassName($classDef->getNamespacedName(false), $flags);
+    }
+
+    protected function checkAccessibleByClassName(string $declaringClass, int $flags): bool
     {
         $scopeClassDef = $this->classDef;
         if ($this->functionDef !== null
@@ -3843,7 +3854,7 @@ class CompilerBase implements PropertyAccessContext
         // 私有方法，只能当前的类使用
         if ($flags & Modifiers::PRIVATE) {
             return $scopeClassDef !== null
-                && strcasecmp($classDef->getNamespacedName(false), $scopeClassDef->getNamespacedName(false)) === 0;
+                && $this->isSameClassName($declaringClass, $scopeClassDef->getNamespacedName(false));
         }
         // 保护方法，只能当前类和子类使用
         if ($flags & Modifiers::PROTECTED) {
@@ -3852,13 +3863,60 @@ class CompilerBase implements PropertyAccessContext
             }
             return $this->canAccessProtectedProperty(
                 $scopeClassDef->getNamespacedName(false),
-                $classDef->getNamespacedName(false)
+                $declaringClass
             );
         }
         // 类外部调用，只允许调用 public 方法
         return true;
     }
 
+    /**
+     * 沿继承链查找实际调用的构造函数，包括项目类继承的内部类构造函数。
+     *
+     * @return array{className: string, flags: int}|null
+     */
+    protected function findConstructor(string $className): ?array
+    {
+        $current = $className;
+        while ($current !== '') {
+            if ($this->hasClass($current)) {
+                $classDef = $this->getClass($current);
+                if ($classDef->hasMethod('__construct')) {
+                    return [
+                        'className' => $classDef->getNamespacedName(false),
+                        'flags' => $classDef->getMethod('__construct')->flags,
+                    ];
+                }
+                $current = $classDef->extends;
+                continue;
+            }
+            if (!$this->isInternalClass($current)) {
+                return null;
+            }
+
+            $constructor = Reflection::getClass($current)?->getConstructor();
+            if ($constructor === null) {
+                return null;
+            }
+            return [
+                'className' => $constructor->getDeclaringClass()->getName(),
+                'flags' => $constructor->getModifiers(),
+            ];
+        }
+        return null;
+    }
+
+    protected function visibilityLabel(int $flags): string
+    {
+        if ($flags & Modifiers::PRIVATE) {
+            return 'private';
+        }
+        if ($flags & Modifiers::PROTECTED) {
+            return 'protected';
+        }
+        return 'public';
+    }
+
     protected function genDebugInfo(?NodeAbstract $stmt = null, string $functionName = '', int $startLine = 0): string
     {
         $code = '';
diff --git a/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt b/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt
new file mode 100644
index 00000000..a1db317b
--- /dev/null
+++ b/tests/compiler/object_ctor/ctor-visibility-protected-subclass.phpt
@@ -0,0 +1,26 @@
+--TEST--
+Constructor visibility - protected constructor accessible from subclass
+--FILE--
+<?php
+
+class Base
+{
+    protected function __construct(){}
+}
+
+class Sub extends Base
+{
+    public static function make(): Base
+    {
+        return new Base();
+    }
+}
+
+function main()
+{
+    $obj = Sub::make();
+    var_dump($obj instanceof Base);
+}
+?>
+--EXPECT--
+bool(true)
diff --git a/tests/compiler/trait/trait-ctor-basic.phpt b/tests/compiler/trait/trait-ctor-basic.phpt
new file mode 100644
index 00000000..1cf76b71
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-basic.phpt
@@ -0,0 +1,27 @@
+--TEST--
+Trait __construct is used by the composing class
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    public function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass();
+}
+?>
+--EXPECT--
+trait ctor
diff --git a/tests/compiler/trait/trait-ctor-override.phpt b/tests/compiler/trait/trait-ctor-override.phpt
new file mode 100644
index 00000000..5b40f487
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-override.phpt
@@ -0,0 +1,32 @@
+--TEST--
+Class __construct overrides the one provided by a trait
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    public function __construct()
+    {
+        echo "trait ctor\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+
+    public function __construct()
+    {
+        echo "class ctor\n";
+    }
+}
+
+function main()
+{
+    new TestClass();
+}
+?>
+--EXPECT--
+class ctor
diff --git a/tests/compiler/trait/trait-ctor-protected-subclass.phpt b/tests/compiler/trait/trait-ctor-protected-subclass.phpt
new file mode 100644
index 00000000..319fd2f3
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-protected-subclass.phpt
@@ -0,0 +1,37 @@
+--TEST--
+Trait protected __construct is accessible from a subclass
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    protected function __construct()
+    {
+        echo "base ctor\n";
+    }
+}
+
+class BaseClass
+{
+    use TestTrait;
+}
+
+class SubClass extends BaseClass
+{
+    public function __construct()
+    {
+        new BaseClass();
+        echo "sub ctor\n";
+    }
+}
+
+function main()
+{
+    new SubClass();
+}
+?>
+--EXPECT--
+base ctor
+sub ctor
diff --git a/tests/compiler/trait/trait-ctor-with-args.phpt b/tests/compiler/trait/trait-ctor-with-args.phpt
new file mode 100644
index 00000000..5177cb28
--- /dev/null
+++ b/tests/compiler/trait/trait-ctor-with-args.phpt
@@ -0,0 +1,30 @@
+--TEST--
+Trait __construct with arguments and $this property access
+--FILE--
+<?php
+
+declare(strict_types=1);
+
+trait TestTrait
+{
+    private int $value = 0;
+
+    public function __construct(int $value)
+    {
+        $this->value = $value;
+        echo "value=" . $this->value . "\n";
+    }
+}
+
+class TestClass
+{
+    use TestTrait;
+}
+
+function main()
+{
+    new TestClass(42);
+}
+?>
+--EXPECT--
+value=42