Despite the rapidly increasing number of female gamers worldwide, female players are still experiencing discrimination, stereotyping, and objectification in digital games. The present study examined the relationships among gender stereotypes, sexism, and sexual harassment in online games, and further investigated how enhanced social presence contributes to intensifying the effects of gender stereotypes and sexism on sexual harassment. An online survey was conducted among 521 young male Korean gamers who regularly play two genres of online games: role-playing games and first-person shooter games. The results of moderated-mediation analyses using Hayes PROCESS macro models confirmed that gender stereotypes had significant effects on hostile and benevolent in-game sexism. A significant interaction was also observed between in-game sexism and social presence in predicting sexual harassment in online games. The findings from this study confirm the role of social presence as an amplifier that reinforces gender stereotypes and discrimination in competitive and violent online game environments.