A method of handling handover message decoding for a mobile device in a wireless communication system is disclosed. The method includes via a first radio access technology (RAT), receiving a handover message associated with a handover from the first RAT to a second RAT supporting services of a packet switched (PS) domain and a circuit switched (CS) domain, wherein the handover message comprises type information and an inter-RAT message generated based on the second RAT, and determining a switched domain type of the inter-RAT message according to the type information.