The use of mouthguards in contact sports effectively prevents oral injury and preserves oral structures. We investigated oral injuries and awareness concerning mouthguards among Japanese high school soccer and rugby players. Athletes were asked a series of questions concerning their history of oral injury while participating in sports, and their pattern of mouthguard use was determined. The data were evaluated statistically using chi-square analysis. The incidence of oral injuries was 32.3% for soccer athletes and 56.5% for rugby athletes, with 0.8% and 24.1% of the respective groups having mouthguards. There were significant differences between the soccer and rugby groups (P < 0.001). Although 81.8% of soccer athletes thought mouthguards were unnecessary, only 26.2% of rugby athletes shared this opinion and there was a significant difference between the soccer and rugby groups. Many soccer athletes had insufficient knowledge about mouthguards and were not concerned about preventing oral injury, although it was in fact a common problem in their sport. Athletes as well as coaches must be made aware of the high risk of oral injury when playing soccer, rugby, and other contact sports.