In this paper, we focus on the effect of power gain imbalance between the H- and V-polarization components, which can boost the overall bit error rate (BER) of a dual-polarization transmission system. Thus, we propose a polarization-domain rotation scheme which rotates the axis of each polarization component such that their power gains are well balanced. In addition, we show that there exist optimal rotation angles which can minimize the BER. Throughout extensive simulation studies, we evaluate the effectiveness of the proposed polarization-domain rotation scheme for various scenarios.