A communication device for handling a signalling radio bearer, SRB, configuration, 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: communicating with a first base station, BS, according to a first SRB configuration, wherein the first SRB configuration configures a first SRB; configuring a first packet data convergence protocol, PDCP, entity associated to the first SRB according to a first PDCP; receiving a first radio resource control, RRC, connection reconfiguration message on the first SRB from the first BS or a second BS using the first PDCP entity; releasing the first PDCP entity associated to the first SRB and configuring a second PDCP entity to apply a second PDCP according to a second SRB configuration different from the first SRB configuration, when the first RRC connection reconfiguration message comprises the second SRB configuration; and transmitting a first RRC connection reconfiguration complete message on the first SRB to a third BS using the second PDCP entity, in response to the first RRC connection reconfiguration message. 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: communicating with a first base station, BS, according to a first SRB configuration, wherein the first SRB configuration configures a first SRB; configuring a first packet data convergence protocol, PDCP, entity associated to the first SRB according to a first PDCP; receiving a first radio resource control, RRC, connection reconfiguration message on the first SRB from the first BS or a second BS using the first PDCP entity; releasing the first PDCP entity associated to the first SRB and configuring a second PDCP entity to apply a second PDCP according to a second SRB configuration different from the first SRB configuration, when the first RRC connection reconfiguration message comprises the second SRB configuration; and transmitting a first RRC connection reconfiguration complete message on the first SRB to a third BS using the second PDCP entity, in response to the first RRC connection reconfiguration message. communicating with a first base station, BS, according to a first SRB configuration, wherein the first SRB configuration configures a first SRB; configuring a first packet data convergence protocol, PDCP, entity associated to the first SRB according to a first PDCP; receiving a first radio resource control, RRC, connection reconfiguration message on the first SRB from the first BS or a second BS using the first PDCP entity; releasing the first PDCP entity associated to the first SRB and configuring a second PDCP entity to apply a second PDCP according to a second SRB configuration different from the first SRB configuration, when the first RRC connection reconfiguration message comprises the second SRB configuration; and transmitting a first RRC connection reconfiguration complete message on the first SRB to a third BS using the second PDCP entity, in response to the first RRC connection reconfiguration message.