Recent incidents in Room n, sexual harassment by social leaders, and the #MeToo movement showed Korea’s immature and distorted sexual culture. This cross-sectional descriptive study investigated the factors affecting the sexual behavior of Korean university students. The participants comprised 258 university students from S and C. The data collection period was from 29 November 2021 to 3 December 2021, and an online survey was conducted on sexual behavior, sexual attitudes, and subject characteristics. The collected data were analyzed using PASW Statistics 25.0. The average age of the participants was 21.38 ± 1.62 years old; the average age when they first watched a pornographic video on YouTube was 14.25 ± 2.55 years old. Sexual behavior was statistically significantly higher for men over 21 and under 14 when they first watched a pornographic video. As the age of the subjects increased, the younger the age of viewing pornographic videos and the thumbnail viewing path of the pornographic videos affected sexual behavior, with an explanatory power of 11.0% (F = 6.27,p< 0.001). Higher sexual attitudes in the communion and permissiveness domains showed greater influence on sexual behavior; the explanatory power was 24.0% (F = 10.02,p< 0.001). Korean university students must be educated on sex early to develop correct sexual attitudes and engage in correct and responsible sexual behaviors in their youth.