The present disclosure relates to a method and apparatus for optimizing mobility robustness by controlling an inter-Radio Access Technology (inter-RAT) factor. A method for supporting inter-Radio Access Network (RAN) mobility by a source Base Station (BS) in a wireless communication system includes transmitting a handover request message to a target BS, receiving a RAN information request message including a measurement report from the target BS in response to the handover request message, and determining to amend a mobility setting, if it is determined that an unnecessary handover has occurred based on the RAN information request message. The handover request message includes at least one of a Tracking Area Identifier (TAI) of a tracking area to which the source BS belongs, a global BS Identifier (ID), and an E-UTRAN (Evolved-UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network) Cell Global ID (ECGI).