Multi-carrier code division multiple access (MC-CDMA) systems receive a great deal of attention due to their great potential in achieving high data rates in wireless communication. Nevertheless, when transmission over fading channel multi-cell interference occurs and this degrades the performance of the system. Site diversity technique is applied to the system to overcome this problem. Due to non orthogonality of spreading codes multi-cell interference is not completely eradicated. In this paper space time block code (STBC) site diversity with multiple input multiple output technique (MIMO) is proposed to improve the performance of MC-CDMA systems and is extended to differential space time block codes (DSTBC). Investigation is done with combining techniques under Rayleigh channel conditions. Simulation results shows that DSTBC outperforms STBC site diversity.