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. <EOS>