Purpose: This study aims at identifying individual- and school-level factors associated with unintentional injuries to Korean adolescents at school by applying multilevel modeling. Methods: From the database of the eleventh Korea Youth Risk Behavior Web-based Survey (KYRBS), the researchers selected 68,043 adolescents from the 7th to the 12th grades. Data were analyzed using x2 test for prevalence and multilevel modeling for related factors of unintentional injuries at school. Results: About 22.9 percent of the adolescents had treatment experiences for unintentional injuries at school in the past 12 months. At the individual level, the significant factors associated with unintentional injuries at school included gender, grade, academic achievement, current smoking, alcohol consumption, frequency of high caffeine intake, depression, and relief of fatigue after sleep. At the group level, the significant factors included number of physical education per week and safety education. Conclusion: School based injury prevention programs should be sensitive to both individual- and school-level factors associated with unintentional injury at school among Korean adolescents.