A method and apparatus change resource allocation to reduce overhead in a mobile communication system. The method of operating a base station for changing a fixed resource allocation to reduce overhead in a mobile communication system includes determining whether a plurality of fixed resource allocations collide in a fixed resource allocation period. If the fixed resource allocations collide, at least one fixed resource allocation among the plurality of fixed resource allocations is cancelled in the fixed resource allocation period and a determination is made on whether to reallocate the at least one fixed resource allocation before a next fixed resource allocation period. If the at least one fixed resource allocation is reallocated before the next fixed resource allocation period, a control message containing reallocation information changed with respect to the at least one fixed resource allocation is transmitted to a corresponding mobile station. Accordingly, a location of an allocation resource region based on a fixed resource allocation can be effectively changed by using minimum control information.