The technical features of this document provide a method and wireless apparatus for performing UE's location area update in a communication system comprising two different radio access network (e.g., E-UTRAN and GERAN/UTRAN). In the communication system, various entities such as MME, VLR, RNC and VLR are included. This document provides a condition when a location area update (LAU) procedure is initiated. In particular, the LAU is performed when the UE which has first performed a combined TAU to the MATE and VLR moves from an E-UTRAN cell to a GERAN/UTRAN cell both belonging to a same location area (LA).