Disclosed is a method and apparatus for determining a controlling PT server. A mobile communication terminal transmits a group generation request message to a PT XDMS, and the PT XDMS determines a specific PT server having the largest number of members as a controlling PT server. The PT XDMS generates group identity information by using an address of the specific PT server, and transmits a group generation response message including the group identity information to the mobile communication terminal. Then, the mobile communication terminal transmits the group identity information of the group generation response message to a PT server with being included in an INVITE message. The PT server certifies the group identity information included in the INVITE message, and determines whether or not itself is to be operated as a controlling PT server.