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. <EOS>