A femtocell, a femtocell gateway and an access rejection method thereof are provided. A wireless network system comprises a wireless device, a plurality of the femtocells, the femtocell gateway and a core network server. The wireless device has a Subscriber Identification and the core network server stores a Closed Subscribers Group Identification of the femtocells. The femtocell gateway receives an access rejection message corresponding to the Subscriber Identification of the wireless device from the core network server, and transmits the access rejection message to the femtocells. Each femtocell records the Subscriber Identification in a rejection list thereof, and it is capable of adding/deleting Subscriber Identifications in its rejection list. When each femtocell receives the Subscriber Identification of the wireless device again and determines that the Subscriber Identification has been recorded in the rejection list thereof, each femtocell immediately terminates a wireless connection from the wireless device.