Under the various conditions such as the positional changes of AP and UT, aspect ratio of the room size, and radiation pattern of UT, we evaluated the channel capacity which depends on AP antenna configuration in indoor MIMO systems by the ray-tracing simulation. As a result, when radiation pattern of UT is isotropic, channel capacity enhancement by directional antennas and orthogonal polarization at the AP was confirmed, and we showed that this improvement was related to the spatial correlation at the AP and received power. This was also verified for the different aspect ratio of the room size. On the other hand, when radiation pattern of UT is considered, the channel capacity enhancement by directional antennas was also confirmed. The discussion for an optimum radiation pattern of UT to make best use of orthogonal polarization is left for the future problem.