diff --git a/homeassistant/components/systemmonitor/sensor.py b/homeassistant/components/systemmonitor/sensor.py
index 4a4703235d3..37059307ef2 100644
--- a/homeassistant/components/systemmonitor/sensor.py
+++ b/homeassistant/components/systemmonitor/sensor.py
@@ -281,8 +281,7 @@ SENSOR_TYPES: dict[str, SysMonitorSensorEntityDescription] = {
     ),
     "last_boot": SysMonitorSensorEntityDescription(
         key="last_boot",
-        translation_key="last_boot",
-        device_class=SensorDeviceClass.TIMESTAMP,
+        device_class=SensorDeviceClass.UPTIME,
         value_fn=lambda entity: entity.coordinator.data.boot_time,
         add_to_update=lambda entity: ("boot", ""),
     ),
diff --git a/homeassistant/components/systemmonitor/strings.json b/homeassistant/components/systemmonitor/strings.json
index 6041dc02c08..97f8f16af84 100644
--- a/homeassistant/components/systemmonitor/strings.json
+++ b/homeassistant/components/systemmonitor/strings.json
@@ -73,9 +73,6 @@
       "ipv6_address": {
         "name": "IPv6 address {ip_address}"
       },
-      "last_boot": {
-        "name": "Last boot"
-      },
       "load_15m": {
         "name": "Load (15 min)"
       },
diff --git a/tests/components/systemmonitor/snapshots/test_sensor.ambr b/tests/components/systemmonitor/snapshots/test_sensor.ambr
index 4bcc0010f24..53ae7dec44c 100644
--- a/tests/components/systemmonitor/snapshots/test_sensor.ambr
+++ b/tests/components/systemmonitor/snapshots/test_sensor.ambr
@@ -146,15 +146,6 @@
 # name: test_sensor[sensor.system_monitor_ipv6_address_eth1 - state]
   'unknown'
 # ---
-# name: test_sensor[sensor.system_monitor_last_boot - attributes]
-  ReadOnlyDict({
-    'device_class': 'timestamp',
-    'friendly_name': 'System Monitor Last boot',
-  })
-# ---
-# name: test_sensor[sensor.system_monitor_last_boot - state]
-  '2024-02-24T15:00:00+00:00'
-# ---
 # name: test_sensor[sensor.system_monitor_load_15_min - attributes]
   ReadOnlyDict({
     'friendly_name': 'System Monitor Load (15 min)',
@@ -413,3 +404,12 @@
 # name: test_sensor[sensor.system_monitor_swap_use - state]
   '60.0'
 # ---
+# name: test_sensor[sensor.system_monitor_uptime - attributes]
+  ReadOnlyDict({
+    'device_class': 'uptime',
+    'friendly_name': 'System Monitor Uptime',
+  })
+# ---
+# name: test_sensor[sensor.system_monitor_uptime - state]
+  '2024-02-24T15:00:00+00:00'
+# ---