diff --git a/tests/ut/test_platform.py b/tests/ut/test_platform.py
index 0f91ca4d..914cd7f4 100644
--- a/tests/ut/test_platform.py
+++ b/tests/ut/test_platform.py
@@ -307,6 +307,26 @@ class TestNPUPlatform(TestBase):
 
         self.assertEqual(vllm_config.cache_config.block_size, 128)
 
+    def test_update_block_size_for_backend_preserves_hybrid_block_size(self):
+        vllm_config = TestNPUPlatform.mock_vllm_config()
+        vllm_config.model_config.is_hybrid = True
+        vllm_config.cache_config.block_size = 1024
+        vllm_config.cache_config.user_specified_block_size = False
+
+        self.platform.update_block_size_for_backend(vllm_config)
+
+        self.assertEqual(vllm_config.cache_config.block_size, 1024)
+
+    def test_update_block_size_for_backend_preserves_user_block_size(self):
+        vllm_config = TestNPUPlatform.mock_vllm_config()
+        vllm_config.model_config.is_hybrid = False
+        vllm_config.cache_config.block_size = 512
+        vllm_config.cache_config.user_specified_block_size = True
+
+        self.platform.update_block_size_for_backend(vllm_config)
+
+        self.assertEqual(vllm_config.cache_config.block_size, 512)
+
     @patch("vllm_ascend.quantization.utils.maybe_auto_detect_quantization")
     @patch("vllm_ascend.utils.get_ascend_device_type", return_value=AscendDeviceType.A3)
     @patch("vllm_ascend.ascend_config.init_ascend_config")
diff --git a/vllm_ascend/platform.py b/vllm_ascend/platform.py
index 55e1408c..0dda6be2 100644
--- a/vllm_ascend/platform.py
+++ b/vllm_ascend/platform.py
@@ -172,6 +172,20 @@ class NPUPlatform(Platform):
     def inference_mode(cls):
         return torch.inference_mode()
 
+    @classmethod
+    def update_block_size_for_backend(cls, vllm_config: VllmConfig) -> None:
+        cache_config = vllm_config.cache_config
+        if cache_config.user_specified_block_size:
+            # User specified --block-size; keep it.
+            return
+        model_config = vllm_config.model_config
+        if model_config is not None and model_config.is_hybrid:
+            # Hybrid attention+mamba models rely on the model-specific sizing
+            # logic rather than the generic platform default.
+            return
+
+        super().update_block_size_for_backend(vllm_config)
+
     @classmethod
     def set_device(cls, device: torch.device):
         torch.npu.set_device(device)