A communication device for handling a resume cause in a radio resource control, RRC, message, comprising: at least one storage device; and at least one processing circuit, coupled to the at least one storage device, wherein the at least one storage device stores instructions, and the at least one processing circuit is configured to execute the instructions of: initiating a RRC resume procedure for a non-access stratum, NAS, requested purpose and a RRC requested purpose, wherein the NAS requested purpose is for performing an emergency service, a high priority access, a mobile terminating access, a mobile originating signaling, a mobile originating data or a mobile originating voice, and the RRC requested purpose is for performing a radio access network, RAN, notification area, RNA, update or for responding to a RAN paging; determining a resume cause in a RRC Resume Request message of the RRC resume procedure according to the RRC requested purpose instead of the NAS requested purpose, if one of the following conditions is satisfied: the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating data; the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating signaling; and the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating voice; otherwise 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 base station, BS, of a network; and receiving a RRC Resume message for responding to the RRC Resume Request message, from the BS. at least one storage device; and at least one processing circuit, coupled to the at least one storage device, wherein the at least one storage device stores instructions, and the at least one processing circuit is configured to execute the instructions of: initiating a RRC resume procedure for a non-access stratum, NAS, requested purpose and a RRC requested purpose, wherein the NAS requested purpose is for performing an emergency service, a high priority access, a mobile terminating access, a mobile originating signaling, a mobile originating data or a mobile originating voice, and the RRC requested purpose is for performing a radio access network, RAN, notification area, RNA, update or for responding to a RAN paging; determining a resume cause in a RRC Resume Request message of the RRC resume procedure according to the RRC requested purpose instead of the NAS requested purpose, if one of the following conditions is satisfied: the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating data; the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating signaling; and the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating voice; otherwise 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 base station, BS, of a network; and receiving a RRC Resume message for responding to the RRC Resume Request message, from the BS. initiating a RRC resume procedure for a non-access stratum, NAS, requested purpose and a RRC requested purpose, wherein the NAS requested purpose is for performing an emergency service, a high priority access, a mobile terminating access, a mobile originating signaling, a mobile originating data or a mobile originating voice, and the RRC requested purpose is for performing a radio access network, RAN, notification area, RNA, update or for responding to a RAN paging; determining a resume cause in a RRC Resume Request message of the RRC resume procedure according to the RRC requested purpose instead of the NAS requested purpose, if one of the following conditions is satisfied: the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating data; the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating signaling; and the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating voice; the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating data; the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating signaling; and the RRC requested purpose is for responding to the RAN paging, and the NAS requested purpose is for performing a mobile originating voice; otherwise 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 base station, BS, of a network; and receiving a RRC Resume message for responding to the RRC Resume Request message, from the BS.