Abstract: Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. Opportunistic Relaying (OR) and Distributed Space-Time Coding (DSTC) are two attractive cooperative diversity schemes. In this study, we introduce a new cooperative scheme: Opportunistic Distributed Space-Time Coding (ODSTC). In ODSTC scheme, more than one relays with best channel conditions are selected. It can achieve a good tradeoff between performance and complexity. We also propose a criterion to select between DSTC scheme and ODSTC scheme. Further, a semi-distributed relay-selection method is given, which can select more than one best relays without topology information.