Distributed video coding (DVC) is one of the new video coding techniques which can fulfill emerging key requirements of low computational complexity and low power consumption at encoder side. Because of different quality among motion-compensated blocks inside side information and effect of quantization, blocking artifacts occur and degrade quality of decoded Wyner-Ziv pictures both subjectively and objectively. In this paper, we propose a deblocking postfilter which aims not only to reduce the uncomfortable artifacts but also to improve coding efficiency by differentiating well-decoded blocks from poorly-decoded ones based on new concept of reliability. Experimental results show that the proposed method not only reduces blocking artifacts considerably but also gains up to 0.23 dB in term of rate distortion (RD) performance.