A communication device for handling dual connectivity, comprising: a storage device, for storing instructions; a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute, the instructions of: configuring, by a first base station, BS, a radio resource control, RRC, connection with a first cell, wherein the first cell belongs to the first BS; receiving a RRC message via the RRC connection on the first cell from the first BS, wherein the RRC message configures a secondary cell group, SCG, configuration to the communication device; synchronizing a downlink, DL, of a second cell in response to the SCG configuration, wherein the second cell belongs to a second BS; and transmitting a RRC complete message to the first cell or a third cell of the first BS in response to the RRC message without performing a random access, RA, procedure to the second cell, if the RRC message indicates no need to perform the RA procedure to the second cell; characterised by determining that the SCG configuration is successfully configured, when detecting a Radio Network Temporary Identifier, RNTI, on a DL channel from the second cell in a first time period. a storage device, for storing instructions; a processing circuit, coupled to the storage device, wherein the storage device stores, and the processing circuit is configured to execute, the instructions of: configuring, by a first base station, BS, a radio resource control, RRC, connection with a first cell, wherein the first cell belongs to the first BS; receiving a RRC message via the RRC connection on the first cell from the first BS, wherein the RRC message configures a secondary cell group, SCG, configuration to the communication device; synchronizing a downlink, DL, of a second cell in response to the SCG configuration, wherein the second cell belongs to a second BS; and transmitting a RRC complete message to the first cell or a third cell of the first BS in response to the RRC message without performing a random access, RA, procedure to the second cell, if the RRC message indicates no need to perform the RA procedure to the second cell; characterised by determining that the SCG configuration is successfully configured, when detecting a Radio Network Temporary Identifier, RNTI, on a DL channel from the second cell in a first time period. configuring, by a first base station, BS, a radio resource control, RRC, connection with a first cell, wherein the first cell belongs to the first BS; receiving a RRC message via the RRC connection on the first cell from the first BS, wherein the RRC message configures a secondary cell group, SCG, configuration to the communication device; synchronizing a downlink, DL, of a second cell in response to the SCG configuration, wherein the second cell belongs to a second BS; and transmitting a RRC complete message to the first cell or a third cell of the first BS in response to the RRC message without performing a random access, RA, procedure to the second cell, if the RRC message indicates no need to perform the RA procedure to the second cell; characterised by determining that the SCG configuration is successfully configured, when detecting a Radio Network Temporary Identifier, RNTI, on a DL channel from the second cell in a first time period.