Abstract: The orthogonal frequency division multiplexing (OFDM) has been regarded as the core technology of 4 G wireless communications system in the future, but the problem of high peak-to-average power ratio (PAPR) is the main obstacle to limit the applications of OFDM. A novel concurrent selective mapping (SLM) algorithm is thus proposed to reduce the PAPR in space-time block coded (STBC) MIMO-OFDM systems. It is proved that the conjugate symbols of two antennas have the same PAPR property, which results in that PAPR reduction to be done is only for the first symbol period. By using the property in the proposed algorithm, the cost due to computational complexity is significantly reduced with the same PAPR performance kept in comparison with the conventional concurrent SLM algorithm. Simulation results demonstrated that the performance of the proposed algorithm outperforms the conventional concurrent SLM algorithm.