Purpose: The purpose of this study was to investigate factors that influence sexual intercourse among middle school students in SouthKorea. Methods: Using statistics from the 8th (2012) Korea Youth Risk Behavior Web-based Survey, hierarchical logistic regression analysiswas conducted. The study sample comprised 37,297 middle school students aged primarily 12 to 15. Results: The significant predictorsof sexual intercourse were grade, ever smoking, ever drinking, habitual or purposeful drug use, economic status, weekly allowance,cohabitation with family, and type of school. Conclusion: The results suggest that intensified sex education is needed not only inthe 1st grade of middle school, but also in the upper grades of elementary school. Sexual health interventions for high-risk groups maybe needed, given the factors predicting sexual intercourse.