An adjustable self-locking wrench is provided. The wrench includes a handle, a base portion having an elongated groove and a locking chamber, a stationary jaw body, a movable jaw having an extension flange, a spring and a locking member. The locking member is movable between a first position wherein the locking member does not tightly contact the extension flange of the movable jaw and a second position wherein the locking member locks the movable jaw in a selected position relative to the stationary jaw.