This letter presents the exact evaluation of the channel capacity difference of different 2 2 multiple-input-multiple-output ( MIMO) handset antenna configurations. In order to investigate the performance enhancement of a MIMO antenna system, the channel capacity is estimated in a reverberation chamber with the normalized channel matrix measured using a network analyzer under the conventional configuration for electromagnetic compatibility/electromagnetic interference (EMC/EMI) evaluations. However, performance comparison of different antenna configurations at the same signal-to-noise ratio (SNR) is not an exact evaluation in the same propagation environment because the received power is obviously different. We propose the evaluation method for exact performance comparisons and drive the exact representation of the channel capacity difference of MIMO handset antenna arrays in a reverberation chamber. The estimated results using the proposed method are compared to the channel capacity evaluated at the same SNR for validation.