diff --git a/runtime/runtime.c b/runtime/runtime.c
index 36ba247..2276bd2 100644
--- a/runtime/runtime.c
+++ b/runtime/runtime.c
@@ -2730,7 +2730,7 @@ op_instanceof: {
     RavaValue_t val = STACK_POP(stack);
     bool result = false;
     if (val.type == RAVA_VAL_OBJECT && val.data.object_val) {
-        result = strcmp(val.data.object_val->class_name, instr->operand.string_value) == 0;
+        result = _rava_vm_instanceof(vm, val.data.object_val->class_name, instr->operand.string_value);
     }
     STACK_PUSH(stack, rava_value_boolean(result));
     DISPATCH();
@@ -4364,7 +4364,7 @@ uf_instanceof: {
     if (rava_nanbox_is_object(val)) {
         RavaObject_t *obj = rava_nanbox_as_object(val);
         if (obj) {
-            result = strcmp(obj->class_name, instr->operand.string_value) == 0;
+            result = _rava_vm_instanceof(vm, obj->class_name, instr->operand.string_value);
         }
     }
     UF_PUSH(rava_nanbox_bool(result));
diff --git a/runtime/runtime_internal.h b/runtime/runtime_internal.h
index 3da58a3..c0c56e1 100644
--- a/runtime/runtime_internal.h
+++ b/runtime/runtime_internal.h
@@ -151,6 +151,7 @@ const char* _rava_intern_string(RavaVM_t *vm, const char *str);
 void _rava_object_set_field_vm(RavaObject_t *obj, const char *name, RavaValue_t value, RavaVM_t *vm);
 
 RavaClass_t* _rava_vm_find_class(RavaVM_t *vm, const char *class_name);
+bool _rava_vm_instanceof(RavaVM_t *vm, const char *object_class, const char *target_class);
 RavaMethod_t* _rava_vm_find_method(RavaVM_t *vm, const char *class_name, const char *method_name);
 RavaMethod_t* _rava_vm_find_method_cached(RavaVM_t *vm, const char *class_name, const char *method_name);
 RavaMethod_t* _rava_vm_find_method_overload(RavaVM_t *vm, const char *class_name, const char *method_name, RavaValue_t *args, size_t arg_count);
diff --git a/runtime/runtime_lookup.c b/runtime/runtime_lookup.c
index cbe8d3e..9eef3e6 100644
--- a/runtime/runtime_lookup.c
+++ b/runtime/runtime_lookup.c
@@ -19,6 +19,19 @@ RavaClass_t* _rava_vm_find_class(RavaVM_t *vm, const char *class_name) {
     return NULL;
 }
 
+bool _rava_vm_instanceof(RavaVM_t *vm, const char *object_class, const char *target_class) {
+    if (!object_class || !target_class) return false;
+    if (strcmp(object_class, target_class) == 0) return true;
+    const char *current = object_class;
+    while (current) {
+        RavaClass_t *cls = _rava_vm_find_class(vm, current);
+        if (!cls) break;
+        if (cls->superclass && strcmp(cls->superclass, target_class) == 0) return true;
+        current = cls->superclass;
+    }
+    return false;
+}
+
 static bool _rava_vm_method_signature_matches(RavaMethod_t *method, RavaValue_t *args, size_t arg_count) {
     if (!method) return false;
     if (method->param_count != arg_count) return false;