A method and apparatus for secondary base station change in a mobile communication system with multiple are provided. Method for secondary node change includes transmitting to a target SN a control message requesting conditional secondary node change, receiving from the target SN a Xn message including conditional secondary node change information, transmitting to a terminal LTE DL message for conditional secondary node change, receiving from the terminal a 1st LTE UL message including a transaction identifier, receiving from the terminal a conditional reconfiguration identifier and transmitting to a source SN a control message for data forwarding.