Previous studies have noted that personality traits are important factors contributing to sexual experiences. Considering this, we examined the associations between the Big Five, narcissism, and sexual narcissism personality traits and multiple dimensions of online sexual activities (OSA). OSAs were classified as viewing sexually explicit material (SEM), seeking sexual partners, cybersex, and flirting. We measured OSA experience, the Big Five, narcissism, and sexual narcissism in 339 participants. The results demonstrated that men reported more OSA engagement than women. Extraversion, openness, neuroticism, narcissism, and sexual narcissism were associated with OSA. Two dimensions of sexual narcissism (sexual exploitation and grandiose sense of sexual skill) mediated the association between gender and OSA. Similarly, sexual exploitation and grandiose sense of sexual skill also mediated the association between narcissism and OSA. The findings indicate that personality traits influence multiple dimensions of OSA. Moreover, sexual narcissism, particularly dimensions of sexual exploitation and grandiose sense of sexual skill, influences OSA more extensively and contribute to gender difference in OSA.