Purpose : This study examined the factors related to sexual intercourse among adolescents in South Korea. Methods : The study sample was comprised of 65,528 middle and high school students aged 12 to 18 years in 2016. For this study, using the data from the 12th Korea youth risk behavior web-based survey, a chi-squared test, and hierarchical logistic regression analysis we reconducted with the SPSS 22.0 program considering personal, family, school, and regional characteristics. Results : The proportion of adolescents who had sexual intercourse was 6.0 % of boys and 2.7 % of girls, and 6.3 % of high school students and 2.4 % of middle school students. The statistically significant related factors of sexual intercourse were gender, grade, attempted suicide, ever drinking, ever smoking, habitual or purposeful drug use, weekly allowance, and coed school in the final model 4. Adolescents with suicide attempts had 2.49 times more sexual intercourse than adolescents with no experience of suicide attempts. Compared to adolescents without alcohol, smoking, and habitual drug use, those who have experienced alcohol, smoking, habitual or purposeful drug use were 2.22 times, 3.76 times, and 3.39 times more likely to have had sexual intercourse, respectively. Adolescents with a weekly allowance of more than 100,000 won per week and adolescents in coed schools were 2.84 times and 1.40 times more likely to have had sexual intercourse, respectively. Conclusion : Multi-level interventions should be considered in school sexual education programs while considering the substantiality of sex education and the actual adolescents' needs. In addition, sexual health interventions in cyberspace for high-risk groups may be needed to consider the emotional and mental characteristics, given the factors related to sexual intercourse in adolescents.