An anchor pretensioner for a vehicle may include a bracket installed at a vehicle body side or a seat side, a cylinder installed on a lower end portion of the bracket, and in which a microgas generator (MGG) for generating explosive pressure is embedded, a rack installed in the cylinder, and moved upward by the explosive pressure, a rotator rotatably installed on an upper end portion of the bracket, engaged with the rack through a gear portion at a lower end of the rotator, and rotated when the rack is moved upward, and a lower anchor plate coupled to an upper end of the rotator, and connected to a webbing.