In this work, we propose a buffer-aided distributed spacetime coding (DSTC) scheme for cooperative direct-sequence codedivision multiple access systems. We first devise a relay selection algorithm that can automatically select the optimum set of relays among both the source-relay phase and the relay-destination phase for DSTC transmission according to the signal-to-interference-plus-noise ratio (SINR) criterion. Multiple relays equipped with buffers are introduced in the network, which allows the relays to store data received from the sources and wait until the most appropriate time for transmission. Simulation results show that the proposed buffer-aided DSTC scheme and algorithm outperform prior art.