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Dynamic resource allocation combined with multiple antennas (MIMO) can farther increase the system capacity and the quality of service (QoS) of conventional OFDM systems. Selection diversity is the simplest way to realize spatial diversity, but the performance improvement of this form of diversity is limited. Adaptive antenna arrays promise to achieve significant increases in system capacity and performance in wireless communications, but they are characterized by a relatively higher implementation complexity than that of selection diversity. In this paper, we propose a dynamic resource allocation scheme with selective beamforming for MIMO/OFDM systems. By applying eigenvalue decomposition on the subset of all available channel correlation matrices, the best beamforming, which corresponds to the largest eigenvalue in the subset, is adaptively selected. Then the proposed dynamic resource allocation algorithm adaptively assigns the bit and power distribution according to the channel gain corresponding to the selected best beamforming, under the constraint of fixed power and overall bit rate. By doing so, the maximal SNR on each sub-carrier obtained by selective beamforming is further maximized. Numerical results show that under frequency-selective multipath fading, the proposed system yields significant performance improvements over the conventional OFDM transmission.