A support assembly includes a base, a slidable member, and a pair of positioning shafts. The base includes at least one sliding rail. The slidable member can side along the at least one sliding rail of the base. The slidable member defines a pair of blind holes facing the base. The positioning shafts can slide along the base in a direction perpendicular to the at least one sliding rail. When the slidable member is operated to slide along the at least one rail of the base, one of the positioning shafts can be pressed to slide along the direction perpendicular to the at least one sliding rail, causing one end of the one of the positioning shafts to be received in one of the blind holes.