A communication device for handling resume causes comprises at least one storage device; and at least one processing circuit coupled to the at least one storage device. The at least one storage device stores instructions, and the at least one processing circuit is configured to execute the instructions of: initiating a radio resource control (RRC) resume procedure for a non-access stratum (NAS) requested purpose and a RRC requested purpose; determining a resume cause in a RRC Resume Request message of the RRC resume procedure according to the NAS requested purpose instead of the RRC requested purpose; transmitting the RRC Resume Request message comprising the resume cause to a BS of the network; and receiving a RRC Resume message for responding to the RRC Resume Request message, from the BS.