In order to ensure a successful inter-system handover, the present invention provides a method for ciphering algorithm change in a wireless communications system. The method includes allowing a ciphering algorithm of a user equipment to be changed during an inter-system handover, where the inter-system handover is preferably a handover from a GSM EDGE radio access network, abbreviated to GERAN, lu mode to a UMTS radio access network, abbreviated to UTRAN.