A method of performing handover of a mobile terminal includes performing a registration procedure by accessing a first network, storing registration information in the first network, and performing handover to a second network upon completion of the registration procedure in order to perform data communication by accessing the second network. The method also includes determining if handover from the second network back to the first network is necessary while the mobile terminal accesses the second network and performing the handover to the first network using the registration information stored in the first network if it is determined that handover from the second network back to the first network is necessary.