This paper proposes an energy and area efficient structure and hardware architecture of FFT processor for 4×4 MIMO-OFDM WLAN systems with four transmit and four receive antennas. Since the basic scheme of MIMO-OFDM system is multiple data transmission, conventional FFT processor for SISO-OFDM system is not suitable for MIMO-OFDM systems. The proposed FFT processor has multi-channel structure to support multiple data path. Multi-channel structure enables to processor several FFT operation with just single processor. Also, by the mixed radix algorithm, the number of non-trivial multiplications of the FFT processor is decreased. The proposed FFT processor reduces the logic gates about 25% over a 4-channel R4MDC FFT processor. Therefore, the proposed FFT processor will contribute improvement to the low power and low complexity design of MIMO-OFDM systems, since the MIMO-OFDM FFT processor is one of the largest modules in the systems, in which the low complexity design is a very important issue.