BackgroundProactive health behaviours are crucial for enhancing adolescent health. However, there is limited evidence on the potential pathways through which social support influences adolescents’ proactive health behaviours. This cross-sectional study aimed to examine the relationships between social support, self-efficacy, peer relationships and proactive health behaviours in Chinese adolescents.MethodsFrom October to December 2023, we recruited 6075 adolescents from Shandong Province, China. They completed self-report questionnaires on social support, self-efficacy, peer relationships and proactive health behaviours.ResultsLinear regression analysis indicated that social support was positively associated with proactive health behaviours among adolescents (β = 0.571, 95% CI = 0.542, 0.600). Further mediation analyses revealed that self-efficacy (β = 0.085, 95% CI = 0.069,0.101) and peer relationships (β = 0.156, 95% CI = 0.136,0.177) mediated this relationship.ConclusionsIncreased social support was associated with better proactive health behaviours in Chinese adolescents. Additionally, higher self-efficacy and positive peer relationships enhanced this association. Our findings emphasised the significance of providing supportive environments at home and at school to promote proactive health behaviours in adolescents.