A charging method for Proximity-based Service (ProSe) used in a first user equipment (UE) of a wireless communication system is disclosed. The charging method includes: establishing a ProSe service with a second UE; generating charging information for the ProSe service according to collected transmission information, wherein the ProSe service is between the first UE and a second UE in proximity and comprises ProSe discovery, ProSe communication or both, and wherein the transmission information comprises at least one of: radio resources dedicated for the ProSe service, allocated to the first UE by the a base station of the wireless communication system; at least one traffic volume report corresponding to uplink or downlink data volume, transmitted to the base station; and a time-elapsed duration for the ProSe service; and transmitting the charging information for the ProSe service to the base station or a core network entity of the wireless communication system.