Provided is a method for operating a co-site by a Base Station (BS) in a mobile communication system. The method includes determining a first number of Mobile Stations (MSs) among MSs connected to a cell to perform handover to a co-site using an Air Resource (AR) utilization of the cell that uses a first Frequency Reuse Pattern (FRP) and an AR utilization of the co-site that uses a second FRP, or determining a second number of MSs among MSs connected to the co-site to perform handover to the cell; and sending a handover initiation message to the MSs according to the determinations.