This paper presents diagonal motion partitions (DMP) for inter prediction in HEVC. In addition to the square and rectangular partitions, we propose to add diagonal shaped partitions to match different motion parts with oblique boundaries. Considering the overlap of pixels along the partition boundaries, the calculation of sum of absolute differences (SAD) and the motion compensation for the pixels on the boundaries are weighted. Besides, the residues of a diagonal prediction unit (PU) are augmented to form a rectangular one, so as to perform Hadamard transform on the residues. We also revise the advanced motion vector prediction (AMVP) and merge candidates based on the diagonal motion partitions. Experimental results show that on average 0.8%-1.0% BD-rate reduction can be achieved by DMP.