MARS-Gait is a new outdoor gait recognition dataset. It is built based on the MARS (Motion Analysis and Re-identification Set) dataset, whose samples are collected in the campus of Tsinghua university. MARS is used for video-based person Re-ID task, which uses 6 near- synchronized cameras located in the campus for recording the pedestrians. It provides the tracklets with person and camera IDs as the annotations. To obtain the gait recognition dataset, we first screened all samples, removing the tracklets where people are obviously not walking, such as cycling or sitting.