A height adjustment apparatus for a vehicle seat may include a pinion gear mounted in a side frame having a front portion and a rear portion are connected to a seat bracket by links; a rack gear engaged with a top end of the pinion gear and coupled with the seat bracket via an hinge, the rack gear moving according to driving of the pinion gear to raise and lower the side frame; and a play adjustment bracket for guiding up and down motion of the moving rack gear by providing repulsive force to a top portion of the rack gear, the play adjustment bracket being fixedly positioned by being fastened with a plurality of support pins provided in the pinion gear and the side frame.