A mechanic's chair with a movable tray includes a support and a seat pad disposed on the support. The tray is disposed below the seat pad and can be pulled to move and engageably fixed in place such that the distance by which the tray is pulled depends on a user's need for accessing the tray for a tool, and the tray is moved and fixed in place efficiently by an engagement mechanism composed of a lever disposed beside the tray and rails disposed on the support.