This thesis proposes a mesh mode for Push-to-Talk over cellular (PoC) service. Through the mesh mode, the users can form a Push-to-Talk session without PoC servers. The detailed message flows for PoC client in mesh mode are also defined. We reuse Talk Burst Control Protocol (TBCP) for control messages and provide a distributed mechanism for floor control. Also, we analyze the group size by a simple model and the performance of the proposed mechanism is validated via simulations. We have also implemented a PoC client in mesh mode and defined a software architecture in this thesis.