Onset of non-suicidal self-injury (NSSI) is most frequent during adolescence. Etiological models indicate that abnormal affective reactivity and regulation within interpersonal contexts is related to heightened NSSI risk. The current study examined the effects of maternal emotional support on adolescent sympathetic nervous system (SNS) activity and observed anger during a conflict discussion among 56 mother-daughter dyads consisting of healthy adolescents and adolescents with a history of self-injury. During the conflict discussion task, maternal emotional support and adolescent anger were coded from behavior, and cardiovascular pre-ejection period was used to index SNS responding. Results demonstrated that maternal emotional support was negatively associated with adolescent anger and SNS activity during the conflict. However, these associations were not significant among adolescents with heightened NSSI history. Maternal emotional support may serve as an interpersonal mechanism for adolescent physiological and behavioral regulation, yet may function differently among adolescents with more frequent NSSI.