A ball bushing positioning structure formed of a sliding rail, a carrier rail, a ball bushing, a release hook and a release control member is disclosed. When inserting the sliding rail with an affixed server into the ball bushing to a certain distance to release stop edges of upright guide walls of a retaining flange of the release hook from the stop walls of the ball bushing subject to the effect of the release control member, the ball bushing is moved with the sliding rail backwardly relative to the carrier rail, preventing falling of the server with the sliding rail out of the carrier rail and avoiding impact between the sliding rail and the ball bushing.