A communication device for handling a bearer type change, 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, and the at least one processing circuit is configured to execute instructions of: receiving a first radio resource control, RRC, message on a signaling radio bearer, SRB, from a first base station, BS, wherein the first RRC message configures a data radio bearer, DRB, which is a secondary cell group, SCG, bearer type or a split bearer type, and configures a first packet data convergence protocol, PDCP, configuration for the DRB; transmitting a first RRC response message to the first BS on the SRB, in response to the first RRC message; establishing a first PDCP entity for the DRB according to the first PDCP configuration; transmitting a first plurality of PDCP Service Data Units, SDUs, to a second BS according to the PDCP entity and a TX_NEXT associated to the PDCP entity; receiving a second RRC message on the SRB from the first BS, wherein the second message configures the DRB from the SCG bearer type or the split bearer type to a master cell group, MCG, bearer type, and configures a second PDCP configuration for the DRB; transmitting a second RRC response message on the SRB to the first BS, in response to the second RRC message; releasing the first PDCP entity, and establishing a second PDCP entity according to the second PDCP configuration; and transmitting a second plurality of PDCP SDUs to the first BS according to the second PDCP entity and a TX HFN and a Next_PDCP_TX_SN associated to the second PDCP entity. 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, and the at least one processing circuit is configured to execute instructions of: receiving a first radio resource control, RRC, message on a signaling radio bearer, SRB, from a first base station, BS, wherein the first RRC message configures a data radio bearer, DRB, which is a secondary cell group, SCG, bearer type or a split bearer type, and configures a first packet data convergence protocol, PDCP, configuration for the DRB; transmitting a first RRC response message to the first BS on the SRB, in response to the first RRC message; establishing a first PDCP entity for the DRB according to the first PDCP configuration; transmitting a first plurality of PDCP Service Data Units, SDUs, to a second BS according to the PDCP entity and a TX_NEXT associated to the PDCP entity; receiving a second RRC message on the SRB from the first BS, wherein the second message configures the DRB from the SCG bearer type or the split bearer type to a master cell group, MCG, bearer type, and configures a second PDCP configuration for the DRB; transmitting a second RRC response message on the SRB to the first BS, in response to the second RRC message; releasing the first PDCP entity, and establishing a second PDCP entity according to the second PDCP configuration; and transmitting a second plurality of PDCP SDUs to the first BS according to the second PDCP entity and a TX HFN and a Next_PDCP_TX_SN associated to the second PDCP entity. receiving a first radio resource control, RRC, message on a signaling radio bearer, SRB, from a first base station, BS, wherein the first RRC message configures a data radio bearer, DRB, which is a secondary cell group, SCG, bearer type or a split bearer type, and configures a first packet data convergence protocol, PDCP, configuration for the DRB; transmitting a first RRC response message to the first BS on the SRB, in response to the first RRC message; establishing a first PDCP entity for the DRB according to the first PDCP configuration; transmitting a first plurality of PDCP Service Data Units, SDUs, to a second BS according to the PDCP entity and a TX_NEXT associated to the PDCP entity; receiving a second RRC message on the SRB from the first BS, wherein the second message configures the DRB from the SCG bearer type or the split bearer type to a master cell group, MCG, bearer type, and configures a second PDCP configuration for the DRB; transmitting a second RRC response message on the SRB to the first BS, in response to the second RRC message; releasing the first PDCP entity, and establishing a second PDCP entity according to the second PDCP configuration; and transmitting a second plurality of PDCP SDUs to the first BS according to the second PDCP entity and a TX HFN and a Next_PDCP_TX_SN associated to the second PDCP entity.