A method for switching data between a plurality of communications systems according to the present invention is characterized by including the steps of: receiving a message from a first communications system having generated at least one data radio bearer (DRB) with a terminal for switching data to a second communications system; switching data to the second communications system based on the message; and carrying out data communication with the base station of the second communications system after switching data, wherein the message contains the information of all DRBs generated in the terminal or the information for indicating whether to keep the information of at least a particular one of the DRBs generated in the terminal, and the data switching operation is performed according to the information.