Multiple-Input Multiple-Output (MIMO) wireless antenna systems have been recognized as a key technology for future wireless communications. The performance of MIMO system can be improved by using multiple antennas at transmitting and receiving side to provide spatial diversity. In this paper, the effects of the number of transmit and receive antennas on the performance of MIMO system over AWGN and Rayleigh fading channels with ZF receiver is analyzed. The bit error rate performance characteristics of Zero-Forcing (ZF) receiver is investigated for M-PSK modulation technique. The AWGN and Rayleigh channels have been used for the analysis purpose and their effect on BER have been presented.