The present invention discloses a mobile device and a power saving method thereof. The mobile device comprises a modem processor and a data processor. The modem processor is electrically connected to a wireless network system for receiving/transmitting a network packet. When the data processor is in a hibernation mode, the IP packet protocol module of the modem processor unpacks the received network packets to access the packet data. If it is determined that the packet data need to be processed by the data processor, the modem processor wakes up the data processor; whereas the data processor remains in the hibernation mode. Thus, the time period in which the data processor is in the hibernation mode is extended so as to achieve power saving effect.