Abstract It is meaningful in practice to explore a secrecy-enhancing Multi-Input-Multi-Output (MIMO) scheme with flexible Radio Frequency (RF) antenna chains as well as low complexity. In this paper, an Artificial Noise (AN) assisted secrecy-enhancing scheme is proposed for the Space–Time Shift Keying (STSK) systems, which has the capability to prevent the passive eavesdropper from eavesdropping the legitimate communication. In the proposed AN-STSK scheme, the transmitter exploits the knowledge of legitimate Channel State Information (CSI) to generate suitable AN with an optimal power fraction in order to introduce interference to the transmit signal. Since the AN resides in the null space of the legitimate channel matrix, the AN can be canceled at the legitimate receiver. First, the secrecy capacity of the proposed AN-STSK scheme has been derived theoretically based on the system model and then resolved by using the Monte Carlo approach. Further, the simulation results of the proposed scheme over the fast fading and block invariant channel have been obtained and studied in detail compared with the traditional AN-Spatial Modulation (SM) scheme. It has been seen that the proposed scheme can improve the secrecy capacity at a cost of a slight increase in Bit Error Rate (BER) through a proper fraction of transmit power allocated to AN. Therefore, the performance trade-offs between the BER and the secrecy capacity can be made in practice. Moreover, it is more effective for the AN-STSK scheme to block the passive eavesdropping when the channel Signal-to-Noise Ratio (SNR) increases since the BER of the legitimate receiver decreases much faster than that of the passive eavesdropper. As a result, the proposed scheme can boost the secrecy capacity at much higher level than the traditional AN-SM scheme in case of the good channel condition.