diff --git a/homeassistant/components/webostv/media_player.py b/homeassistant/components/webostv/media_player.py
index c8b871b3bf2..076b6caad24 100644
--- a/homeassistant/components/webostv/media_player.py
+++ b/homeassistant/components/webostv/media_player.py
@@ -284,6 +284,9 @@ class LgWebOSMediaPlayerEntity(RestoreEntity, MediaPlayerEntity):
             if model := self._client.system_info.get("modelName"):
                 self._attr_device_info["model"] = model
 
+            if serial_number := self._client.system_info.get("serialNumber"):
+                self._attr_device_info["serial_number"] = serial_number
+
         self._attr_extra_state_attributes = {}
         if self._client.sound_output is not None or self.state != MediaPlayerState.OFF:
             self._attr_extra_state_attributes = {
diff --git a/tests/components/webostv/conftest.py b/tests/components/webostv/conftest.py
index bf007f5b936..c6594746cc5 100644
--- a/tests/components/webostv/conftest.py
+++ b/tests/components/webostv/conftest.py
@@ -42,7 +42,7 @@ def client_fixture():
         client = mock_client_class.return_value
         client.hello_info = {"deviceUUID": FAKE_UUID}
         client.software_info = {"major_ver": "major", "minor_ver": "minor"}
-        client.system_info = {"modelName": TV_MODEL}
+        client.system_info = {"modelName": TV_MODEL, "serialNumber": "1234567890"}
         client.client_key = CLIENT_KEY
         client.apps = MOCK_APPS
         client.inputs = MOCK_INPUTS
diff --git a/tests/components/webostv/snapshots/test_diagnostics.ambr b/tests/components/webostv/snapshots/test_diagnostics.ambr
index a9bd6e91ee0..07ee50af1f8 100644
--- a/tests/components/webostv/snapshots/test_diagnostics.ambr
+++ b/tests/components/webostv/snapshots/test_diagnostics.ambr
@@ -41,6 +41,7 @@
       'sound_output': 'speaker',
       'system_info': dict({
         'modelName': 'MODEL',
+        'serialNumber': '1234567890',
       }),
     }),
     'entry': dict({
diff --git a/tests/components/webostv/snapshots/test_media_player.ambr b/tests/components/webostv/snapshots/test_media_player.ambr
index 35a703cc109..23f45a0f325 100644
--- a/tests/components/webostv/snapshots/test_media_player.ambr
+++ b/tests/components/webostv/snapshots/test_media_player.ambr
@@ -61,7 +61,7 @@
     'name': 'LG webOS TV MODEL',
     'name_by_user': None,
     'primary_config_entry': <ANY>,
-    'serial_number': None,
+    'serial_number': '1234567890',
     'suggested_area': None,
     'sw_version': 'major.minor',
     'via_device_id': None,