ObjectiveTo explore the association between social support, parent-child relationships, and depression, anxiety, and loneliness among adolescents, in order to provide a reference for improving mental health in youth.MethodsA total of 11,596 middle school students from two districts of Shanghai were investigated with the stratified random cluster sampling method. The Chinese version of Patient Health Questionnaire (PHQ-2-C), Generalized Anxiety Disorder (GAD-7), UCLA Loneliness Scale (ULS-6), Perceived Social Support Scale and Parent-child Cohesion Questionnaire were used in the survey. Statistical inferences were made using t-test, ANOVA, and logistic regression analysis.ResultsGirls, non-graduates, students ranking in the top 25%, adolescents living with parents and with higher socioeconomic status had higher scores of social support and parent-child cohesion than boys, graduates, students ranking in the middle or in the bottom 25%, adolescents not living with parents and with lower socioeconomic status (P