diff --git a/homeassistant/components/uptime/sensor.py b/homeassistant/components/uptime/sensor.py
index db06b09ea18..9a48b09e452 100644
--- a/homeassistant/components/uptime/sensor.py
+++ b/homeassistant/components/uptime/sensor.py
@@ -50,4 +50,4 @@ class UptimeSensor(SensorEntity):
         self._attr_name: str = name
         self._attr_device_class: str = DEVICE_CLASS_TIMESTAMP
         self._attr_should_poll: bool = False
-        self._attr_native_value: str = dt_util.now().isoformat()
+        self._attr_native_value = dt_util.now()