This paper proposes a compact and low-profile multi-input multi-output (MIMO) terminal antenna employing the bidirectional Yagi-Uda array. The parasitic antennas that function as a director are designed to maximize the MIMO channel capacity. A parasitic antenna optimization method, in which a 'parasitic channel' is defined, is also proposed. This method is effective in finding the optimum design with a very low computational load. Based on numerical analysis of an indoor environment, the proposed and optimally designed antenna enhances the channel capacity by more than 10% compared to an antenna without parasitic elements even when the space for the antennas is limited such as in a PC card terminal.