In this paper, performance of STBC, VBLAST, MLSTBC and Hybrid-STBC-VBLAST is investigated in the presence of rayleigh fading for relay assisted multiple access communication. STBC provides diversity gain but does not provide multiplexing gain. On the other hand, VBLAST provides multiplexing gain but does not provide diversity gain. But combination of STBC and VBAST scheme such as MLSTBC and HYBRID-STBC-VBLAST provide both diversity and multiplexing gain. So, it is possible to improve the capacity of second hop for a relay assisted multiple access channel maintaining the reliability of system by using MLSTBC or Hybrid-STBC-VBLAST. The capacity of whole system also increases for using MLSTBC and HYBRID-STBC-VBLAST at relay. An adaptive MIMO transmission approach among STBC, VBLAST, MLSTBC and Hybrid-STBC-VBLAST is also proposed based on the capacity for relay assisted multiple access communication. The proposed scheme compares the capacity of STBC, VBLAST, MLSTBC and Hybrid-STBC-VBLAST at destination and selects the MIMO mode for highest capacity and sends feedback to the relay with two extra signaling bits. It consists of users where each user transmits STBC encoded information from two transmit antennas. STBC or VBLAST or MLSTBC or Hybrid-STBC-VBLAST is used depending on the feedback bits to re-encode the information at relay. Simulation and analytical results are presented to show the performance of the proposed system.