IPTV is a system based on IP network, which may include service by a broadband connection. In this sense, it is possible to provide various multimedia contents by using IP network with interactivity. However, since IPTV service quality may be easily affected by network degradation such as packet loss, jitter, and so on, the quality of IPTV service may not be guaranteed. In this paper, we propose an objective measure for blocking artifacts, which is one of the most important impairments experienced when enjoying IPTV. Experimental results show that the proposed measure correlates well with the subjective evaluation.