An operation method in heterogeneous networks, and a gateway and a wireless communication device using the same are disclosed. The operation method in heterogeneous networks includes followings. When a gateway, connecting a first communication network and a second communication network, operates in a beacon mode, the gateway determines whether the first communication network is in an allowed period or a forbidden period, and generates a determination result. Then, the gateway adaptively adjusts a ratio of a superframe duration to a beacon interval of a periodic beacon of the second communication network according to the determination result. In addition, the gateway is connected to a M2M communication server via the first communication network, and the gateway is connected to at least one M2M communication device via the second communication network.