A vise jaw is provided, including: a first jaw, including a slide groove and at least one locking portion, each locking portion including a receiving room, a threaded hole and a through hole, the receiving room, the threaded hole and the through hole respectively communicated with each other; a second jaw, having a slide protrusion slidably disposed within the slide groove, the slide protrusion having a lateral face facing the through hole; at least one fastening assembly, each fastening assembly including a screw member, an abutting member and at least one elastic member, the screw member screwed into the threaded hole, the abutting member adjustably disposed within the receiving room, the abutting member including a large diameter section and a small diameter section which are arranged along a first direction, the small diameter section disposed through the through hole and extending into the slide groove.