A drive over mower deck automatic locking mechanism includes a lift frame engaging a drive over mower deck, and a pair of locking plates pivotably connected to the lift frame. The locking plates lock the drive over mower deck to the lift frame when the lift frame raises the drive over mower deck to a mowing or transport position, and unlock the drive over mower deck from the lift frame when the lift frame lowers the drive over mower deck to an installation position.