A locking mechanism for a folding knife includes a thumb post which longitudinally moves along slots in the handle of the knife. The thumb post is urged by a spring loaded locking lever into a notch in the base of the blade of the knife. When so positioned the thumb post retains the blade in an extended position. When the user pushes the thumb post out of the notch, the blade can be folded into the handle of the knife. In another embodiment the thumb post is an integral part of the locking lever, and it is a tab on the locking lever rather than the thumb post engages the notch in the base of the blade.