The present disclosure discloses a method for managing user information in an instant messaging system in order to address the problems of increasing system workload, increasing network overhead and deteriorated system performance in existing technologies due to frequent access of user information management server or servers when user information is searched. According to a disclosed method, an access server obtains and stores information of contacts of a logged-in user; the access server notifies user information of the logged-in user to other access servers; the access servers that receive the notification store the user information of the logged-in user upon determining that contact(s) is/are found locally therein; and when the access server needs to obtain the information of the contacts of the user, the access server performs a search either locally or in other access servers. Furthermore, a communication system is also provided. The disclosed method and system are believed to result in greatly reduced frequency of searching user information in the user information management servers, reduced workload of the user information management servers, improved performance of searching user information and reduced network overhead of the system.