A communication device for handling a redirection, 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 is configured to store, and the at least one processing circuit is configured to execute, instructions of: connecting to a core network, CN, node network through a first cell of a first base station, BS, of a New Radio, NR; transmitting an Internet Protocol, IP, Multimedia Subsystem, IMS, signaling message to the CN node via the first BS; receiving a redirection message from the first BS of the NR via the first cell, wherein the redirection message comprises RAT information indicating an Evolved Universal Terrestrial Radio Access, E-UTRA, and indicates the 5GC network or an Evolved Packet Core, EPC, network; entering an idle state in response to the redirection message; selecting a second cell of the E-UTRA according to the RAT information; establishing a radio resource control, RRC, connection via the second cell to a second BS, wherein the second BS is connected to the 5GC network and the EPC network; generating a non-access-stratum, NAS, message for the 5GC network or the EPC network according to the RAT information and the indication of 5GC or EPC; and transmitting the NAS message on the RRC connection via the second cell to the second 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 is configured to store, and the at least one processing circuit is configured to execute, instructions of: connecting to a core network, CN, node network through a first cell of a first base station, BS, of a New Radio, NR; transmitting an Internet Protocol, IP, Multimedia Subsystem, IMS, signaling message to the CN node via the first BS; receiving a redirection message from the first BS of the NR via the first cell, wherein the redirection message comprises RAT information indicating an Evolved Universal Terrestrial Radio Access, E-UTRA, and indicates the 5GC network or an Evolved Packet Core, EPC, network; entering an idle state in response to the redirection message; selecting a second cell of the E-UTRA according to the RAT information; establishing a radio resource control, RRC, connection via the second cell to a second BS, wherein the second BS is connected to the 5GC network and the EPC network; generating a non-access-stratum, NAS, message for the 5GC network or the EPC network according to the RAT information and the indication of 5GC or EPC; and transmitting the NAS message on the RRC connection via the second cell to the second BS. connecting to a core network, CN, node network through a first cell of a first base station, BS, of a New Radio, NR; transmitting an Internet Protocol, IP, Multimedia Subsystem, IMS, signaling message to the CN node via the first BS; receiving a redirection message from the first BS of the NR via the first cell, wherein the redirection message comprises RAT information indicating an Evolved Universal Terrestrial Radio Access, E-UTRA, and indicates the 5GC network or an Evolved Packet Core, EPC, network; entering an idle state in response to the redirection message; selecting a second cell of the E-UTRA according to the RAT information; establishing a radio resource control, RRC, connection via the second cell to a second BS, wherein the second BS is connected to the 5GC network and the EPC network; generating a non-access-stratum, NAS, message for the 5GC network or the EPC network according to the RAT information and the indication of 5GC or EPC; and transmitting the NAS message on the RRC connection via the second cell to the second BS.