Abstract: A transmit mode switching (TMS) assisted adaptive spatial modulation (SM) scheme is proposed for multiple-input multiple-output (MIMO) transmission systems. The proposed scheme yields a performance bound with the aid of the nearest neighbor approximation. At a predefined spectral efficiency and transmit power target, the proposed scheme is capable of selecting the appropriate SM mode to minimize the conditioned pairwise error probability. Moreover, a simplified calculation method utilizing the special information transmission method of SM is proposed for mode selection. Simulation results show that the proposed scheme exhibits a better bit error ratio (BER) performance at low complexity cost compared with the conventional SM scheme, especially for the correlated MIMO channels.