diff --git a/python_module/megengine/module/module.py b/python_module/megengine/module/module.py
index d91fa94ec84e418f24b926f1df0cd6a6b1b9f489..b55bdd89446a52529d8b657f99537975132ddd7f 100644
--- a/python_module/megengine/module/module.py
+++ b/python_module/megengine/module/module.py
@@ -291,19 +291,21 @@ class Module(metaclass=ABCMeta):
             if param.grad is not None:
                 param.grad.reset_zero()
 
-    def train(self, mode: bool = True) -> None:
+    def train(self, mode: bool = True, recursive: bool = True) -> None:
         """Set training mode of all the modules within this module (including itself) to
         ``mode``. This effectively sets the ``training`` attributes of those modules
         to ``mode``, but only has effect on certain modules (e.g.
-        :class:`~.BatchNorm2d`, :class:`~.Dropout`)
+        :class:`~.BatchNorm2d`, :class:`~.Dropout`, :class:`~.Observer`)
 
-        :param mode: The training mode to be set on modules.
+        :param mode: the training mode to be set on modules.
+        :param recursive: whether to recursively call submodules' ``train()``.
         """
-        self.training = mode
+        if not recursive:
+            self.training = mode
+            return
 
-        def fn(x) -> None:
-            if x is not self:
-                x.train(mode=mode)
+        def fn(module: Module) -> None:
+            module.train(mode, recursive=False)
 
         self.apply(fn)
 
diff --git a/python_module/megengine/quantization/observer.py b/python_module/megengine/quantization/observer.py
index 847cc814106316ec7d6178ab198d92f1e9f7f87a..bbd7c234f05107754a43477cde3c89a6a988944a 100644
--- a/python_module/megengine/quantization/observer.py
+++ b/python_module/megengine/quantization/observer.py
@@ -60,8 +60,8 @@ class Observer(Module):
     def disable(self):
         self.enabled = False
 
-    def train(self, mode: bool = True) -> None:
-        super().train(mode)
+    def train(self, mode: bool = True, recursive: bool = True) -> None:
+        super().train(mode, recursive)
         if mode:
             self.enable()
         else: