A base station, a femtocell, and a handover monitoring method thereof are provided. A wireless network system comprises a server, a mobile device, the base station, and the femtocell. The base station transmits a monitoring signal to the femtocell after it obtains a piece of information corresponding to the mobile device from the server. The femtocell keeps detecting whether a signal is transmitted by the mobile device after it receives the monitoring signal. The femtocell transmits a response signal corresponding to the monitoring signal to the base station after it detects the signal transmitted by the mobile device. The base station transmits a handover signal to the mobile device after it receives the response signal so that the mobile device handovers from the base station to the femtocell. A handover monitoring from the base station to the femtocell for the mobile device is provided by the hand monitoring method.