Broadband wireless packet access will be the core technology of the next generation mobile communication systems. For very high-speed and high-quality packet transmissions, the joint use of multiple-input multiple-output (MIMO) multiplexing and hybrid ARQ (HARQ) is very effective. However, if single-carrier (SC) transmission is used, the transmission performance significantly degrades due to a large inter-symbol interference (ISI) resulting from a severe frequency-selective fading. Recently, we proposed a frequency-domain iterative parallel interference cancellation (PIC) for SC-MIMO multiplexing. For signal separation, 2 dimensional minimum mean square error (2D MMSE)-FDE is performed at first. Then, the joint PIC and ID MMSE-FDE is repeated a sufficient number of times. However, the interference from other transmit antennas still remains at the outputs of PIC. Therefore, in this paper, we propose to use 2D MMSE-FDE instead of ID MMSE-FDE in each iteration and investigate, by computer simulation, the achievable bit error rate (BER) and throughput performance of HARQ in a frequency-selective Rayleigh fading channel.