Purpose: This study aims to examine the factors influencing sexually transmitted infection (STI) in Korean adoles-cents 12 to 18 years. Methods: Using statistics from 10-11th Korea Youth Risk Behavior Web-based Survey, secon-dary analysis was conducted. The study sample consisted of 4,886 boys and 1,998 girls who had reported initiating sexual intercourse. Results: The proportion of adolescents who had a sexually transmitted infection was 8.8% of boys and 11.0% of girls. In multiple regression analysis, grade, smoking, first intercourse before middle school, inter-course after drinking alcohol, living without family, large amounts of pocket money were factors associated with sex-ually transmitted infection for both boys and girls. Use of condom is related to STI contraction of boys only. Formal sex education was not associated with reducing risk of STI. Conclusion: The results of this study show the factors associated with STI among Korean adolescents. Gender-related effective interventions should be taken into consid-eration in school-based sex education programs.