A support structure for a ball screw includes a base, two pivot seats mounted on the base, a screw disposed between the two pivot seats, at least one guide rail fixed on the base, a first guide block fixed on the base and provided with a first slanting surface, a second guide block fixed on the base and provided with a second slanting surface, a support seat slidably mounted on the guide rails and located below the screw, a nut unit sleeved on the screw and slidably disposed on the guide rails, and a drive assembly fixed at the nut unit. The support structure for a ball screw has a simple structure, a low maintenance cost and a longer service life.