A buckle for a sports boot, such as an alpine ski boot, as well as a sports boot equipped with such buckle. The buckle is adapted to move two parts of the boot upper relative to each other for tightening the boot on the foot and/or lower leg of the wearer, the buckle including a base fixed on the first of the boot parts, a lever articulated on the base, and a hooking element connected to the lever by means of a rod. The lever contour demarcates a surface, the area of which is greater than 27 cm.sup.2 and the width thereof being greater than 53 mm. The buckle also includes a rack fixed to the second of the parts of the boot, the width of which is greater than 25 mm. With a buckle having such dimensions, a ski boot according to the invention can be equipped with only two such buckles, one on the lower base and one on the cuff.