Aim: Non-suicidal self-injury (NSSI) is common among adolescents, and several different factors can affect its prevalence. The present study examined the associated characteristics predicting NSSI among adolescents in South Korea. Methods: In total, 1674 high school students were recruited for a cross-sectional survey. They completed self-reported assessments, including the Deliberate Self-Harm Inventory (DSHI), the Center for Epidemiological Studies Depression Scale (CESD), the State-Trait Anxiety Inventory for Children (STAIC), and the Prodromal Questionnaire-16 (PQ-16), as well as their bullying experience. The NSSI group was defined as the sample group with at least one NSSI behaviour on the DSHI scale. A logistic regression analysis was performed using the NSSI group as the dependent variable. Results: The prevalence of NSSI was 28.3% (boys, 30.4%; girls, 24.4%) among adolescents. The most common type of NSSI behaviour among adolescents was interference with wound healing and sex differences in the method were examined. The CES-D, STAIC-trait, and PQ-16 scores were significantly higher and the RSES score was significantly lower in the NSSI group than those in the non-NSSI group. Participants' experience with bullying, such as being victims, bullies, bully-victims, and witness to bullying, were more likely to be in the NSSI group. In a logistic regression analysis, NSSI was significantly associated with male sex, low academic achievement, higher depression, psychotic-like experiences, being bullied, and witnessing bullying. Conclusion: The results of this study suggest the need to identify and manage related psychologic factors in adolescents with NSSI, including psychotic-like symptoms.