Abstract: Objective To explore the relationship among personality,self-efficacy and mental health in left-behind junior high school students.Methods Totally 459 left-behind and 241 non left-behind junior high school students were investigated with the Five-Factor Personality Questionnaire,General Self-Efficacy Scale and the Mental Health Test.Results The incidence rate of mental disorders was 1.1% in the left-behind junior high school students.The top three mental problems were terror tendency (29.0%),self reproach (28.1%) and physical symptoms (21.4%).Significant gender differences were found in physical symptom (6.02±2.59 for boys,6.68±2.54 for girls),terror tendency (3.28 ±2.50 for boys,4.70±2.60 for girls),and the total score of mental problems (41.95±11.65 for boys,44.73±11.32 for girls) among the left-behind students (all P< 0.01).Self-efficacy had negative function (adjusted R²=0.045) in predicting the mental problem among the left-behind students.Neuroticism,extraversion,and conscientiousness could be used to predict mental problems(adjusted R²=0.235).Conclusion Besides shaping positive personality,the training of self-efficacy can improve mental health status among the left-behind junior high school students.