Abstract: This invention provides a child safety seat with an integral seat belt tensioner for properly securing the seat to the passenger seat of an automotive vehicle by taking up the slack in the seat belt after it has been fastened through the child seat. The tensioner pulls or pushes the seat belt so that the few inches of slack that usually exist are eliminated by the tensioner. The safety seat is adapted to have internal space, either in its back and/or below the seat, to accommodate the tensioner and the belt movement so that the controls, tensioner, and/or other moving parts are out of the reach of the a child in the seat. A preferred version of the tensioner includes motor and gearing to move a belt holder up and down generally along the rear of the safety seat, for tightening and loosening the belt, respectively.