Mouthguards are essential in the prevention of athletic oral/facial injuries. The mouthguards are typically made from plastic materials such as an ethylene vinyl acetate copolymer (EVA). The present study was undertaken to evaluate four kinds of commercial mouthguards and investigate the effects of vinyl acetate (VA) content on the mechanical properties of EVA. In the result of FT-IR, it was found that all commercial mouthguards used in this study were made of EVA. The impact strengths of all commercial mouthguards were 40~70 J/m. As the VA content increased in the EVA, the elongation of EVA was increased and the tensile strength was decreased. EVA with high VA content showed soft rubber-like properties. The impact strength of EVA was decreased with increase of VA content. From these results, the VA content was very important factor for controlling the mechanical properties of EVA mouthguard material, especially impact resistance.