A mobile communication system and a mobile station service method in the mobile communication system is disclosed, and enables mobile terminals of a second generation (IS-95, IS-95B) and a third generation (IS-2000) to be operated using a CDMA Channel List and an Extended CDMA Channel List. The method preferably includes checking whether a frequency on service presently exists on a CDMA Channel List and an Extended CDMA Channel List when a service frequency of a base station is changed, copying the frequency allocated to the Extended CDMA Channel List to the CDMA Channel List if the frequency on service fails to exist on the CDMA Channel List, copying the frequency allocated to the CDMA Channel List to the Extended CDMA Channel List if the frequency on service fails to exist on the Extended CDMA Channel List, and transmitting the CDMA and Extended CDMA Channel Lists to which the frequency is copied to a terminal.