This Master thesis is about multicast in mobile network 3rd generation UMTS(Universal Mobile Telecommunacitions System). UMTS network primary designs for data transfers and supports new services as real-time transfers of multimedia streams. This is reason why mobile network was equiped also with multicast service. When a lot of users want to receive same data (e.g. tv program) the network excessives load of transmission same data and the server have to keep connection to each user. Group 3GGP developed multicast service for UMTS, which name is MBMS (Multimedia Broadcast and Multicast Service). Thesis analyses function of this service in mobile network. First part describes basic principles of UMTS network and its structure. Next part focuses on change of main node (SGSN and GGSN) and of new node BM-SC(Broadcast-Multicast Service Center). This new node is main node for control of multicast transmission. BM-SC connects to server which provides multicast data for users and provisions individual phase of MBMS session. It was created new procedure which supports multicast session (e.g. Activate MBMS service). Next part focuses on GPRS Tunneling Protocol (GTP). This protocol is used for transfers control and user’s data in tunnels inside core network. This part describes structure of data and control messages. Last part analyzes multimedia transfers in UMTS with program Opnet Modeller.