Abstract: The foldable blade knife comprises a blade with a tang positioned between the arms of a flat U-shaped handle at the ends of the arms away from the base of the handle, and a pivot pin extends through the arms of the handle and through the tang equidistant from the butt of the tang and the ends of the arms. The handle defines an opening sized and shaped to approximately correspond to the size and shape of the blade element, and at least one edge surface of the tang and the facing surface of an arm of the handle are formed in interfitting convex-concave shapes so that the resilient arms of the handle tend to hold the blade folded into the handle or to hold the blade extending out coextensively from the handle and when the handle is grasped by a hand, the gripping force by the hand tends to further lock the blade in its open or closed positions.