diff --git a/mackerel-client.cabal b/mackerel-client.cabal
--- a/mackerel-client.cabal
+++ b/mackerel-client.cabal
@@ -1,5 +1,5 @@
 name:                   mackerel-client
-version:                0.0.3
+version:                0.0.4
 author:                 itchyny
 maintainer:             itchyny <https://github.com/itchyny>
 license:                MIT
diff --git a/src/Web/Mackerel/Types/Monitor.hs b/src/Web/Mackerel/Types/Monitor.hs
--- a/src/Web/Mackerel/Types/Monitor.hs
+++ b/src/Web/Mackerel/Types/Monitor.hs
@@ -90,6 +90,7 @@
   = MonitorHost {
     monitorId :: Maybe MonitorId,
     monitorName :: String,
+    monitorMemo :: Maybe String,
     monitorDuration :: Integer,
     monitorMetric :: String,
     monitorOperator :: MonitorOperator,
@@ -103,6 +104,7 @@
   | MonitorConnectivity {
     monitorId :: Maybe MonitorId,
     monitorName :: String,
+    monitorMemo :: Maybe String,
     monitorIsMute :: Maybe Bool,
     monitorNotificationInterval :: Maybe Integer,
     monitorScopes :: Maybe [String],
@@ -111,6 +113,7 @@
   | MonitorService {
     monitorId :: Maybe MonitorId,
     monitorName :: String,
+    monitorMemo :: Maybe String,
     monitorService :: String,
     monitorDuration :: Integer,
     monitorMetric :: String,
@@ -123,6 +126,7 @@
   | MonitorExternal {
     monitorId :: Maybe MonitorId,
     monitorName :: String,
+    monitorMemo :: Maybe String,
     monitorMethod :: Maybe MonitorExternalMethod,
     monitorUrl :: String,
     monitorRequestBody :: Maybe String,
@@ -142,6 +146,7 @@
   | MonitorExpression {
     monitorId :: Maybe MonitorId,
     monitorName :: String,
+    monitorMemo :: Maybe String,
     monitorExpression :: String,
     monitorOperator :: MonitorOperator,
     monitorWarning :: Double,
diff --git a/test/Types/MonitorSpec.hs b/test/Types/MonitorSpec.hs
--- a/test/Types/MonitorSpec.hs
+++ b/test/Types/MonitorSpec.hs
@@ -14,6 +14,7 @@
   let hostMonitor = MonitorHost {
         monitorId = Just $ MonitorId "abcde1",
         monitorName = "Monitor custom.foo.bar",
+        monitorMemo = Just "Monitor memo",
         monitorDuration = 5,
         monitorMetric = "custom.foo.bar",
         monitorOperator = MonitorGreaterThan,
@@ -30,6 +31,7 @@
       "type": "host",
       "id": "abcde1",
       "name": "Monitor custom.foo.bar",
+      "memo": "Monitor memo",
       "duration": 5,
       "metric": "custom.foo.bar",
       "operator": ">",
@@ -45,6 +47,7 @@
   let connectivity = MonitorConnectivity {
         monitorId = Just $ MonitorId "abcde2",
         monitorName = "connectivity",
+        monitorMemo = Just "Monitor memo",
         monitorIsMute = Just False,
         monitorNotificationInterval = Nothing,
         monitorScopes = Nothing,
@@ -56,6 +59,7 @@
       "type": "connectivity",
       "id": "abcde2",
       "name": "connectivity",
+      "memo": "Monitor memo",
       "isMute": false
     }
   |]
@@ -63,6 +67,7 @@
   let serviceMonitor = MonitorService {
         monitorId = Just $ MonitorId "abcde3",
         monitorName = "Service count",
+        monitorMemo = Just "Monitor memo",
         monitorService = "service1",
         monitorDuration = 5,
         monitorMetric = "custom.service.count",
@@ -78,6 +83,7 @@
       "type": "service",
       "id": "abcde3",
       "name": "Service count",
+      "memo": "Monitor memo",
       "service": "service1",
       "duration": 5,
       "metric": "custom.service.count",
@@ -92,6 +98,7 @@
   let externalMonitor = MonitorExternal {
         monitorId = Just $ MonitorId "abcde4",
         monitorName = "Example external monitor",
+        monitorMemo = Just "Monitor memo",
         monitorMethod = Just MonitorExternalMethodGET,
         monitorUrl = "https://example.com",
         monitorRequestBody = Just "Request Body",
@@ -114,6 +121,7 @@
       "type": "external",
       "id": "abcde4",
       "name": "Example external monitor",
+      "memo": "Monitor memo",
       "method": "GET",
       "url": "https://example.com",
       "requestBody": "Request Body",
@@ -135,6 +143,7 @@
   let expressionMonitor = MonitorExpression {
         monitorId = Just $ MonitorId "abcde5",
         monitorName = "Example expression monitor",
+        monitorMemo = Just "Monitor memo",
         monitorExpression = "min(role(\"foo:bar\", \"custom.foo.bar\"))",
         monitorOperator = MonitorLessThan,
         monitorWarning = 10.0,
@@ -148,6 +157,7 @@
       "type": "expression",
       "id": "abcde5",
       "name": "Example expression monitor",
+      "memo": "Monitor memo",
       "expression": "min(role(\"foo:bar\", \"custom.foo.bar\"))",
       "operator": "<",
       "warning": 10.0,