The use of multiple antennas is another major element of any 5G cellular system because it will be possible to alter the beam direction to enable more direct communications and limit interference and increase overall cell capacity. Among techniques in the area of multiple antennas, MB-MIMO (Multi beam-Multiple Input Multiple Output) technique gains a lot of attention due to the performance improvement with the possibility of real implementation. However, in literature, the consideration of MB-MIMO technique does not concern the 120 degree sector. Even in 5G cellular, the practical installation of base station might still be 120 degree sector. Hence, this paper presents the performance analysis of MB-MIMO under 120 degree sector considerations. The simulation results indicate the interesting issue on number of optimum beams for MB-MIMO that the 120 degree sector considerations requires less beams than conventional cell. This can lead to the real implementation for 5G technology in the near future.