OBJECTIVE: During the transition from late childhood into adolescence, parents' support of their children's autonomy plays an increasingly important role in facilitating healthy emotion regulation and protecting children against the development of internalizing problems. Although theoretical work suggests that fathers' autonomy support may be particularly protective, little empirical work has explored the effects of fathers' autonomy support on internalizing problems. The present study focused on the relations between fathers' autonomy support and adolescent internalizing problems, as well as whether there were interactions between paternal and maternal autonomy support on adolescent adjustment. DESIGN: Using multilevel modeling with person-mean centering, the present study examined the between- and within-person effects of fathers' and mothers' autonomy support on youth- and parent-reported internalizing problems in a three-wave longitudinal sample of 298 fathers, mothers, and children ( child age at time 1 = 11 years old, 51.5% girls). RESULTS: Negative between- and within-person effects of paternal autonomy support emerged on adolescents' internalizing problems. The between- and within-person effects of paternal autonomy on youth- and father-reported internalizing problems also interacted with maternal autonomy support. Additionally, two findings suggested that fathers' autonomy support was most beneficial in the presence of higher levels of maternal support, mothers' autonomy support was optimized in the presence of higher paternal support, and maternal support could buffer against the effects of low levels of paternal support. CONCLUSIONS: Fathers may best help buffer and protect children against internalizing problems by fostering healthy emotion regulation via support of autonomy.