Abstract: A lock apparatus for a chain grab hook comprises a locking member adapted to be pivotally attached to the clevis of the chain grab hook about a pivot element located between a mid-point of the locking member and the top surface of the clevis. When installed, a bias element is operative to exert a bias force on the locking member urging the front end of the locking member to pivot upward to a closed position wherein the front end of the locking member extends into the open end of the jaw a sufficient distance to prevent a chain link engaged in the jaw from moving out of the open end of the jaw. The front end of the locking member can be pushed downward against the bias force to an open position to release the chain link from the jaw.