Disclosed herein are a multicasting system and method for a vehicular communication network. The multicasting system includes a plurality of roadside communication devices for communicating with a plurality of vehicular communication devices. Each of the roadside communication devices includes a communication unit for communicating with the plurality of vehicular communication devices and at least one neighboring roadside communication device, a beacon analysis unit for analyzing beacon frames when a slot allocation request is received from one of the vehicular communication devices, a determination unit for searching for a period in which a slot has not been allocated and determining whether a period for allocation of a slot to the vehicular communication device is present, and a slot allocation unit for allocating a slot period for multicasting of the vehicular communication device based on results of the determination of the determination unit.