Purpose: Recognizing the positive influence of forgiveness on adolescent development, this study investigated the effectiveness of a forgiveness intervention in reducing peer victimization and enhancing forgiveness levels among left-behind and non-left-behind junior high school students in China. Methods: Based on the Enright process-based model, 72 students (36 left-behind) were randomly assigned to intervention or control groups. Over 4 weeks, 70 students completed eight sessions, with peer victimization and forgiveness levels assessed at pretest, posttest, and 2-month follow-up. Results: The forgiveness intervention reduced peer victimization (ps < .001) and boosted forgiveness (ps < .001) in both groups but was more effective for non-left-behind students than their left-behind peers (p = .016). Conclusions: Forgiveness interventions are effective in mitigating peer victimization and fostering forgiveness, particularly for students in supportive environments. Tailored approaches are needed for left-behind students to enhance effectiveness. Future studies should address extended interventions and broader demographic factors.