A new and improved turbo processing multi-input multi-output (MIMO) system using a non-linear minimum mean square error (MMSE) detector is proposed. Based on the non-linear mean square (MS) estimation, the a posteriori information of a soft-input soft-output (SISO) decoder is fed back to the MMSE detector instead of the extrinsic information. Unlike a MAP (Maximum a Posteriori) detector, the MMSE detector shows no error propagation caused from using the a posteriori as an a priori information. The proposed turbo process with non-linear MMSE detector needs a posteriori information, which is easily obtained from turbo SISO decoder without increasing receiver complexity. The performance of the proposed method is compared with conventional methods by using computer simulation in a Mobile Wimax system environment.