diff --git a/homeassistant/components/aemet/weather_update_coordinator.py b/homeassistant/components/aemet/weather_update_coordinator.py
index a9af8f25f1c..a7ca0a12422 100644
--- a/homeassistant/components/aemet/weather_update_coordinator.py
+++ b/homeassistant/components/aemet/weather_update_coordinator.py
@@ -283,7 +283,7 @@ class WeatherUpdateCoordinator(DataUpdateCoordinator):
         temperature_feeling = None
         town_id = None
         town_name = None
-        town_timestamp = dt_util.as_utc(elaborated)
+        town_timestamp = dt_util.as_utc(elaborated).isoformat()
         wind_bearing = None
         wind_max_speed = None
         wind_speed = None
diff --git a/tests/components/aemet/test_sensor.py b/tests/components/aemet/test_sensor.py
index b265b996709..7887139a386 100644
--- a/tests/components/aemet/test_sensor.py
+++ b/tests/components/aemet/test_sensor.py
@@ -127,7 +127,7 @@ async def test_aemet_weather_create_sensors(hass):
     assert state.state == "Getafe"
 
     state = hass.states.get("sensor.aemet_town_timestamp")
-    assert state.state == "2021-01-09 11:47:45+00:00"
+    assert state.state == "2021-01-09T11:47:45+00:00"
 
     state = hass.states.get("sensor.aemet_wind_bearing")
     assert state.state == "90.0"