To provide a mouth guard capable of being comfortably worn with the optimal occlusion provided by a simple method without requiring an exclusive device according to a method of manufacturing the mouth guard to be used for preventing burdens on the jaw tissue or preventing external injury to the jaws at the time of sports.

The mouth guard is manufactured by waxing the shape of the mouth guard in a dentition model 1; making a mold 4 of a material for the mold, such as autopolymerizing resin; boring two holes, an injection hole 6 and a discharge hole 7, in the mold; covering the dentition model 1 with the mold; and injecting an elastic material such as room-temperature addition-polymerization silicone into the dentition model 1.