When ZigBee network supports beacon transmission mechanism, ZigBee devices have the restriction of the transmission range from the coordinator. On the contrary, when it does not support beacon transmission, it is not easy to save the energy through turning into sleep mode. This paper proposes active slot allocation method that allocates a transmission time and does not use the beacon transmission mechanism. It is based on the ZigBee's distributed address assignment mechanism and supports the scalability. This paper explains the active slot structure and the allocation order and describes the operation of ZigBee devices. We verify the proposed mechanism through the simulation and show the performance evaluation. It can be useful on the industrial automation and the environmental surveillance.