["Family Relations, EarlyView. ", "\nAbstract\n\nObjective\nThis study aimed to examine whether and how life satisfaction mediates, and growth mindset moderates, the associations between family environment and adolescent nonsuicidal self‐injury (NSSI) and suicidality among boys and girls.\n\n\nBackground\nPositive family environment demonstrated protective effects against adolescent self‐harming intentions and behaviors. Emerging evidence suggested that overall life satisfaction and mindsets toward negative emotions play critical roles in these relationships, with potential gender‐specific variations.\n\n\nMethod\nData were from a large‐scale, two‐wave school survey with a 1‐year interval (N = 3,151) in Hong Kong. Descriptive statistics, correlations, and mediation and moderation models were employed to investigate the interaction mechanisms separately among girls and boys.\n\n\nResults\nCompared to girls, boys reported lower prevalence of NSSI and suicidality, higher life satisfaction, and stronger growth mindsets. A positive family environment was found to reduce NSSI, suicidal ideation, and suicidal attempt by enhancing adolescents' life satisfaction. Growth mindset amplified the protective effects of positive family environment, with gender differences observed: It moderated the longitudinal association between family environment and life satisfaction among boys (p = .011), and the direct link to suicidal attempt in girls (p = .036).\n\n\nConclusion\nThe study highlighted the protective mechanisms of positive family environments and life satisfaction on NSSI and suicidality, alongside heterogeneous moderation of growth mindset across genders.\n\n\nImplications\nThere is a need to advance more nuanced theoretical frameworks of adolescent development. Moreover, both life satisfaction and growth mindset represent promising targets for intervention and policy development, with attention to gender‐sensitive pathways recommended to optimize effectiveness.\n\n"]