diff --git a/cores/esp8266/Esp.cpp b/cores/esp8266/Esp.cpp
index a0e5c6f418..3416c9b913 100644
--- a/cores/esp8266/Esp.cpp
+++ b/cores/esp8266/Esp.cpp
@@ -329,6 +329,28 @@ bool EspClass::checkFlashConfig(bool needsEquals) {
     return false;
 }
 
+String EspClass::getResetReason(void) {
+    char buff[32];
+    if (resetInfo.reason == REASON_DEFAULT_RST) { // normal startup by power on 
+      strcpy_P(buff, PSTR("Power on"));
+    } else if (resetInfo.reason == REASON_WDT_RST) { // hardware watch dog reset
+      strcpy_P(buff, PSTR("Hardware Watchdog"));
+    } else if (resetInfo.reason == REASON_EXCEPTION_RST) { // exception reset, GPIO status won’t change 
+      strcpy_P(buff, PSTR("Exception"));
+    } else if (resetInfo.reason == REASON_SOFT_WDT_RST) { // software watch dog reset, GPIO status won’t change 
+      strcpy_P(buff, PSTR("Software Watchdog"));
+    } else if (resetInfo.reason == REASON_SOFT_RESTART) { // software restart ,system_restart , GPIO status won’t change 
+      strcpy_P(buff, PSTR("Software/System restart"));
+    } else if (resetInfo.reason == REASON_DEEP_SLEEP_AWAKE) { // wake up from deep-sleep 
+      strcpy_P(buff, PSTR("Deep-Sleep Wake"));
+    } else if (resetInfo.reason == REASON_EXT_SYS_RST) { // external system reset 
+      strcpy_P(buff, PSTR("External System"));
+    } else {
+      strcpy_P(buff, PSTR("Unknown"));
+    }
+    return String(buff);
+}
+
 String EspClass::getResetInfo(void) {
     if(resetInfo.reason != 0) {
         char buff[200];
diff --git a/cores/esp8266/Esp.h b/cores/esp8266/Esp.h
index f04dd0e4d4..405a94c8ee 100644
--- a/cores/esp8266/Esp.h
+++ b/cores/esp8266/Esp.h
@@ -131,6 +131,7 @@ class EspClass {
         uint32_t getFreeSketchSpace();
         bool updateSketch(Stream& in, uint32_t size, bool restartOnFail = false, bool restartOnSuccess = true);
 
+        String getResetReason();
         String getResetInfo();
         struct rst_info * getResetInfoPtr();
 
diff --git a/doc/changes.md b/doc/changes.md
index 1855121d50..bed0289f1f 100644
--- a/doc/changes.md
+++ b/doc/changes.md
@@ -6,6 +6,7 @@ title: Change Log
 
 ### Core
 
+- Add function to know last reset resaon.
 - Allow control of enabling debug and debug level from IDE
 - Make HardwareSerial::begin() and end() interrupt safe
 - Put HardwareSerial and cbuf methods called from interrupt context in RAM
diff --git a/doc/libraries.md b/doc/libraries.md
index 210171ec6e..22e913babe 100644
--- a/doc/libraries.md
+++ b/doc/libraries.md
@@ -83,6 +83,8 @@ APIs related to deep sleep and watchdog timer are available in the `ESP` object,
 
 `ESP.restart()` restarts the CPU.
 
+`ESP.getResetReason()` returns String containing the last reset resaon in human readable format.
+
 `ESP.getFreeHeap()` returns the free heap size.
 
 `ESP.getChipId()` returns the ESP8266 chip ID as a 32-bit integer.
diff --git a/tools/sdk/include/user_interface.h b/tools/sdk/include/user_interface.h
index 470556c706..81868563b0 100644
--- a/tools/sdk/include/user_interface.h
+++ b/tools/sdk/include/user_interface.h
@@ -23,13 +23,13 @@
 #endif
 
 enum rst_reason {
-	REASON_DEFAULT_RST		= 0,
-	REASON_WDT_RST			= 1,
-	REASON_EXCEPTION_RST	= 2,
-	REASON_SOFT_WDT_RST   	= 3,
-	REASON_SOFT_RESTART 	= 4,
-	REASON_DEEP_SLEEP_AWAKE	= 5,
-	REASON_EXT_SYS_RST      = 6
+	REASON_DEFAULT_RST		= 0,	/* normal startup by power on */
+	REASON_WDT_RST			= 1,	/* hardware watch dog reset */
+	REASON_EXCEPTION_RST	= 2,	/* exception reset, GPIO status won’t change */
+	REASON_SOFT_WDT_RST   	= 3,	/* software watch dog reset, GPIO status won’t change */
+	REASON_SOFT_RESTART 	= 4,	/* software restart ,system_restart , GPIO status won’t change */
+	REASON_DEEP_SLEEP_AWAKE	= 5,	/* wake up from deep-sleep */
+	REASON_EXT_SYS_RST      = 6		/* external system reset */
 };
 
 struct rst_info{