A method and apparatus for canceling a triggered proximity-based services (ProSe) buffer status report (BSR) in a wireless communication system is provided. A user equipment (UE) triggers at least one ProSe BSR, and cancels all triggered ProSe BSR if a specific condition is met. The specific condition may be that a device-to-device (D2D) scheduling assignment for a D2D scheduling period can accommodate all pending data available for D2D transmission or that the ProSe BSR is included in a media access control (MAC) protocol data unit (PDU) to be transmitted to a network.