Disclosed are a method and apparatus for keeping orders among messages when transmitting and receiving messages within a Converged IP Messaging (CPM) session. A message transmission and reception method in a network comprises receiving a message including sequential identification information and a cumulative size, and outputting the received message, wherein the sequential identification information is an identifier allowing identification of orders managed within a session, transmission and reception being performed in the session, and the cumulative size is the sum of sizes of messages, the messages being sent by a subject having sent the received message within the session, wherein the output order of the received message is decided based upon the sequential identification information and sequential identification information relating to messages received prior to the received message.