A lawn mower deck opening guard includes an underbody plate, a reversed angle flange, a first mounting flange, and a second mounting flange. The reversed angle flange is connected to the underbody plate through a front free edge of the underbody plate while the first mounting flange and the second mounting flange are respectively connected to the underbody plate through a first fixed edge and a second fixed edge of the underbody plate. The lawn mower deck opening guard utilizes a plurality of fasteners to connect with a mower deck of a lawn mower through the first mounting flange and the second mounting flange. The reversed angle flange and the underbody plate are then able to improve the safety of the operator and control the debris expulsion during the mowing process.
