diff --git a/moto/iot/models.py b/moto/iot/models.py
index 14289a00d..1ebce5eaa 100644
--- a/moto/iot/models.py
+++ b/moto/iot/models.py
@@ -883,7 +883,7 @@ class IoTBackend(BaseBackend):
             if not do_merge:
                 thing.attributes = attributes
             else:
-                thing.attributes.update(attributes)
+                thing.attributes = {k: v for k, v in attributes.items() if v}
 
     def create_keys_and_certificate(
         self, set_as_active: bool
@@ -1307,7 +1307,6 @@ class IoTBackend(BaseBackend):
         return thing_names
 
     def list_thing_principals(self, thing_name: str) -> List[str]:
-
         things = [_ for _ in self.things.values() if _.thing_name == thing_name]
         if len(things) == 0:
             raise ResourceNotFoundException(
diff --git a/tests/test_iot/test_iot_things.py b/tests/test_iot/test_iot_things.py
index 65f605ea5..773bdab3e 100644
--- a/tests/test_iot/test_iot_things.py
+++ b/tests/test_iot/test_iot_things.py
@@ -54,6 +54,15 @@ def test_update_thing():
     assert res["things"][0]["thingArn"] is not None
     assert res["things"][0]["attributes"]["k1"] == "v1"
 
+    client.update_thing(
+        thingName=name, attributePayload={"attributes": {"k1": ""}, "merge": True}
+    )
+    res = client.list_things()
+    assert len(res["things"]) == 1
+    assert res["things"][0]["thingName"] is not None
+    assert res["things"][0]["thingArn"] is not None
+    assert res["things"][0]["attributes"] == {}
+
 
 @mock_iot
 def test_describe_thing():