A circuit breaker interlock mechanism interacts between the circuit breaker operating handle and circuit breaker closing button to prevent the closing button from operating to close the circuit breaker contacts when the circuit breaker is padlocked in the OFF condition. A slide plate mounted on the interior of the circuit breaker cover engages a blocking plate attached to the circuit breaker closing rod. The interlock serves further to prevent the circuit breaker from being padlocked on the ON condition in the event the contacts become welded together in the closed position.