diff --git a/aiogram/dispatcher/fsm/state.py b/aiogram/dispatcher/fsm/state.py
index d4ea1974..ced9779a 100644
--- a/aiogram/dispatcher/fsm/state.py
+++ b/aiogram/dispatcher/fsm/state.py
@@ -111,8 +111,8 @@ class StatesGroupMeta(type):
             return item in cls.__all_states_names__
         if isinstance(item, State):
             return item in cls.__all_states__
-        # if isinstance(item, StatesGroup):
-        #     return item in cls.__all_childs__
+        if isinstance(item, StatesGroupMeta):
+            return item in cls.__all_childs__
         return False
 
     def __str__(self) -> str:
@@ -126,8 +126,11 @@ class StatesGroup(metaclass=StatesGroupMeta):
             return cls
         return cls.__parent__.get_root()
 
-    # def __call__(cls, event: TelegramObject, raw_state: Optional[str] = None) -> bool:
-    #     return raw_state in cls.__all_states_names__
+    def __call__(cls, event: TelegramObject, raw_state: Optional[str] = None) -> bool:
+        return raw_state in type(cls).__all_states_names__
+
+    def __str__(self) -> str:
+        return f"StatesGroup {type(self).__full_group_name__}"
 
 
 default_state = State()
diff --git a/tests/test_dispatcher/test_fsm/test_state.py b/tests/test_dispatcher/test_fsm/test_state.py
index 07037e86..04c8e448 100644
--- a/tests/test_dispatcher/test_fsm/test_state.py
+++ b/tests/test_dispatcher/test_fsm/test_state.py
@@ -139,8 +139,7 @@ class TestStatesGroup:
         assert MyGroup.state1 not in MyGroup.MyNestedGroup
         assert MyGroup.state1 in MyGroup
 
-        # Not working as well
-        # assert MyGroup.MyNestedGroup in MyGroup
+        assert MyGroup.MyNestedGroup in MyGroup
 
         assert "MyGroup.MyNestedGroup:state1" in MyGroup
         assert "MyGroup.MyNestedGroup:state1" in MyGroup.MyNestedGroup
@@ -150,3 +149,36 @@ class TestStatesGroup:
         assert 42 not in MyGroup
 
         assert MyGroup.MyNestedGroup.get_root() is MyGroup
+
+    def test_empty_filter(self):
+        class MyGroup(StatesGroup):
+            pass
+
+        assert str(MyGroup()) == "StatesGroup MyGroup"
+
+    def test_with_state_filter(self):
+        class MyGroup(StatesGroup):
+            state1 = State()
+            state2 = State()
+
+        assert MyGroup()(None, "MyGroup:state1")
+        assert MyGroup()(None, "MyGroup:state2")
+        assert not MyGroup()(None, "MyGroup:state3")
+
+        assert str(MyGroup()) == "StatesGroup MyGroup"
+
+    def test_nested_group_filter(self):
+        class MyGroup(StatesGroup):
+            state1 = State()
+
+            class MyNestedGroup(StatesGroup):
+                state1 = State()
+
+        assert MyGroup()(None, "MyGroup:state1")
+        assert MyGroup()(None, "MyGroup.MyNestedGroup:state1")
+        assert not MyGroup()(None, "MyGroup:state2")
+        assert MyGroup.MyNestedGroup()(None, "MyGroup.MyNestedGroup:state1")
+        assert not MyGroup.MyNestedGroup()(None, "MyGroup:state1")
+
+        assert str(MyGroup()) == "StatesGroup MyGroup"
+        assert str(MyGroup.MyNestedGroup()) == "StatesGroup MyGroup.MyNestedGroup"