A hard handover method and a Radio Network Controller (RNC) therefor in a mobile telecommunication system are provided which can improve the performance of an interfrequency hard handover. The RNC stores information about a timing difference between first and second Node Bs for supporting a soft handover. When receiving, from a User Equipment (UE), a request for a hard handover from the first Node B to the second Node B, the RNC computes information about a timing difference between the Node Bs for the hard handover using the information about the timing difference between the Node Bs stored at a soft handover time. The RNC commands the second Node B and the UE to operate for the hard handover using the computed timing difference information.