Disclosed is a notification system and method using messenger. The system includes a messenger system for controlling instant message transmission, monitoring messenger user state change, and transmitting user state change information; an external service system for monitoring occurrence of events and generating notification message indicating occurrence of the events; and a synchronization server for receiving the user state change information from the messenger system, providing the received user state change information to the at least one external service system, receiving the notification message from the at least one external service system, and transmitting the notification message to the messenger system. The external service system receives the user state change information from the synchronization server and manages messenger user online information, in case of the event occurrence.