To handle downlink data upon handover of a user equipment from a source base station to a target base station in a wireless communications system, the source base station forwards a plurality of radio link control (RLC) service data units (SDUs) or RLC protocol data units (PDUs) that have not been positively acknowledged by the user equipment to the target base station. Then, the target base station sends the plurality of RLC SDUs or RLC PDUs to the user equipment.