Abstract: A fire hydrant locking device comprises a clamp which engages the hydrant stem and includes apertured butterfly wings which are engaged by a forked rod locking the stem in a closed position. The rod extends through a donut to engage a tubular recess in the cap. Spring loaded curved pins engage the rod within the tubular recess and extend outwardly through the cap. A wrench having a circular recess with inward projections engages the cap pins to permit turning the threaded cap and permit access to the locked stem for actuation of the hydrant.