This study explored the effect of emotion regulation styles - integrative emotion regulation (IER), suppressive emotion regulation, and dysregulation-on adolescents' psychosocial adjustment following a Covid-19-related lockdown. 114 mother-adolescent dyads were surveyed after lockdown and at two additional time points (three and six months later). Adolescents were aged 10-16years, 50.9% females. Adolescents reported on their emotion regulation styles. Mothers and adolescents reported on adolescents' well-being (depressive symptoms, negative and positive emotions) and social behaviour (aggression and prosocial behaviour). Results of multilevel linear growth models showed IER predicted optimal well-being and social behaviour reported by both mothers and adolescents at baseline and a self-reported reduction in prosocial behaviours over time. Suppressive emotion regulation predicted reduced self-reported well-being after lockdown, evident in higher levels of negative affect and depressive symptoms and reductions in mother-reported prosocial behaviour over time. Dysregulation predicted reduced well-being and impaired social behaviour after lockdown, reported by both mothers and adolescents, and a reduction in self-reported depressive symptoms over time. Results suggest adolescents' adjustment to lockdown was affected by their habitual emotion regulation styles.