The present invention relates to a method of UE mobility management and a mobile communication system of implementing this method, where the system includes: a core network communicating with the universal terrestrial radio access network (UTRAN) via the Iu interface; UTRAN consisting of multiple radio network systems (RNS) and communicating with one or more UE via the Uu interface, and each said RNS comprising a radio network controller (RNC) and one or more nodes communicating with said RNC via the Iub interface, while communication between RNC being performed via the Iur interface; UTRAN controlling UE mobility management through radio resource control (RRC) signalling of the Uu interface; and said method includes: UE transmitting uplink RRC signalling information to a first RNC to request UE mobility management; the first RNC receiving and forwarding said uplink RRC signalling information to the core network; the core network forwarding transparently said uplink RRC signalling information to a second RNC; and the second RNC receiving and utilizing said uplink RRC signalling information to perform the required mobility management.