This communication game system comprises a client system 1 and a game server system 2 for communicating with the client system 1. The game server system 2 comprises a database 21 for storing group information which relates a plurality of client systems to each other as a battle group. The game server system 2 is structured to decide a battle combination among the client systems 1 belonging to the same battle group, to perform a battle by managing the sending and receiving of data between the client systems determined by the above-mentioned combination, and to decide the next combination in accordance with the results of the battle. Each client system 1 has its own character select function and chat function when watching games.