A method and a system for performing a group call using unicast and multicast are provided. A group call method performed by a first client device, may include: establishing a media session with a server providing a group call service based on a group call request from the first client device; transmitting, to the server through the media session, at least one first packet including a first source identifier of the first client device; providing a user interface at the first client device, that enables selecting at least one second client device from a plurality of second client devices that participate in a group call initiated by the first client device; and transmitting, from the first client device to the server, at least one second packet including a second source identifier of the selected at least one second client device as a destination of data included in the at least one second packet.