In this paper, we focus on detecting data hiding in motion vectors of compressed video and propose a new steganalytic algorithm based on the mutual constraints of motion vectors. The constraints of motion vectors from multiple frames are analyzed and formulized by three functions, then statistical features are extracted based on these functions. Moreover, we also incorporate calibration method to improve the detection accuracy. Experimental results demonstrate that the proposed method can effectively attack typical motion-vector-based video steganography. © 2013 IEEE.