A method of handling a cell addition for dual connectivity in a communication system comprising a communication device, a first base station and a second base station, the communication device being connected to the first base station, the method being utilized in the first base station and comprising: transmitting a request message to the second base station, for requesting a cell addition for the communication device (302, 402); receiving a response message comprising system information of a cell of the second base station from the second base station in response to the request message (304, 404); transmitting a first radio resource control, RRC, message comprising the system information to the communication device, after receiving the response message (306, 406); and receiving a RRC response message from the communication device in response to the first RRC message; wherein the system information comprises an uplink configuration of the cell and/or a downlink configuration of the cell; wherein the uplink configuration comprises at least one of an uplink carrier frequency, an uplink bandwidth, additional spectrum emission, a parameter p-Max, an uplink power control, a sounding uplink reference signal configuration, an uplink cyclic prefix length, a physical random access channel configuration, a physical uplink shared channel configuration, a random access channel configuration and a time-division duplexing, TDD, configuration; and wherein the downlink configuration comprises at least one of at least one of a downlink bandwidth, antenna information, a multicast-broadcast single-frequency network subframe configuration, a physical HARQ indicator channel configuration, a physical downlink shared channel configuration and a time-division duplexing, TDD, configuration. transmitting a request message to the second base station, for requesting a cell addition for the communication device (302, 402); receiving a response message comprising system information of a cell of the second base station from the second base station in response to the request message (304, 404); transmitting a first radio resource control, RRC, message comprising the system information to the communication device, after receiving the response message (306, 406); and receiving a RRC response message from the communication device in response to the first RRC message; wherein the system information comprises an uplink configuration of the cell and/or a downlink configuration of the cell; wherein the uplink configuration comprises at least one of an uplink carrier frequency, an uplink bandwidth, additional spectrum emission, a parameter p-Max, an uplink power control, a sounding uplink reference signal configuration, an uplink cyclic prefix length, a physical random access channel configuration, a physical uplink shared channel configuration, a random access channel configuration and a time-division duplexing, TDD, configuration; and wherein the downlink configuration comprises at least one of at least one of a downlink bandwidth, antenna information, a multicast-broadcast single-frequency network subframe configuration, a physical HARQ indicator channel configuration, a physical downlink shared channel configuration and a time-division duplexing, TDD, configuration.