It is a challenge to prove whether or not a digital video has been tampered with. In this paper, we propose a novel approach to detection of double MEPG compression which often occurs in digital video tampering. The doubly MPEG compressed video will demonstrate different intrinsic characteristics from the MPEG video which is compressed only once. Specifically, the probability distribution of the first digits of the non-zero MPEG quantized AC coefficients will be disturbed. The statistical disturbance is a good indication of the occurrence of double video compression, and may be used as tampering evidence. Since the MPEG video consists of I, P and B frames and double compression may occur in any or all of these different types of frames, the first digit probabilities in frames of these three types are chosen as the first part of distinguishing features to capture the changes caused by double compression. In addition, the fitness of the first digit distribution with a parametric logarithmic law is tested. The statistics of fitting goodness are selected as the second part of the distinguishing features. We propose a decision rule using group of pictures (GOP) as detection unit. The proposed detection scheme can effectively detect doubly MPEG compressed videos for both variable bit rate (VBR) mode and constant bit rate (CBR) mode.