Transmission network expansion planning (TNEP) is a basic part of power network expansion planning. Up to now, various papers have been presented on the field of static transmission network expansion planning (STNEP). But, in all of them, the effect of load growth on the network loss in transmission networks with different voltage levels has not been investigated. Therefore, in this paper, STNEP has been studied considering the effect of load growth factor on the network loss in a transmission network with two different voltage levels using genetic algorithm (GA). Finally the proposed idea is examined on Garverpsilas six-bus network. The results show that the load growth factor has important effect on the network loss rate and subsequent type of the network arrangement.