This paper describe MU-MIMO testbed which can deal with 16 times 16 MIMO-OFDM transmission based on the IEEE802.11a signal format. This testbed can be used to evaluate various antenna configurations, transmission schemes, scheduling algorithms, and so on, because the software and the antennas in this testbed can be flexibly changed. By using this testbed, we have evaluated the frequency utilization for a downlink transmission in the MU-MIMO channel in an actual indoor environment. We clarified that the MU-MIMO transmission using a block diagnarization algorithm achieved a frequency utilization of over 30 bits/s/Hz. The frequency utilization of the MU-MIMO transmission with two users is 2.1 to 3.3 times higher compared with the eigenvector beamforming method in SU-MIMO, when the number of transmit antenna is fixed to 16 and the number of receive antennas is changed from 2 to 4.