Abstract: This study provides an insight into the selective Decode-Forward (DF) relaying based Multiple-Input-Multiple-Output (MIMO)-Space-Time Block-Coded (STBC) cooperative wireless communication system with single and multiple relays over Nakagami-m fading channels, considering the effect of channel estimation error. Firstly, we examine the Symbol Error Rate (SER) performance at equal power allocation. Secondly, we have analyzed the SER performance at the optimal power allocation case and compare the Symbol Error Rate (SER) performance at equal power allocation and optimal power allocation case. Lastly, we have analyzed the symbol error rate performance with increasing number of relays.