OBJECTIVE: Maternal postpartum depression (PPD) may influence fathers' engagement in childrearing; however, empirical studies have been equivocal as to whether these effects emerge in a compensatory (i.e., higher paternal engagement) or spillover (i.e., lower paternal engagement) manner. This study evaluated fathers' gender role attitudes as a moderator that shapes the association between maternal PPD and fathers' engagement during infancy, and also examined relations between father engagement and children's subsequent behavior problems. METHOD: In a prospective study of low-income, Mexican-origin families (N = 181 mothers and a subset of their partners, N = 92 fathers), maternal PPD symptoms and fathers' gender role attitudes were measured at 15-weeks postpartum, father engagement was measured at 21-weeks, and children's behavior problems were measured at 12 and 18 months. RESULTS: Higher maternal PPD symptoms were associated with lower father engagement and more child behavior problems when fathers endorsed more segregated gender role attitudes; however, this relation was not significant when fathers endorsed less segregated, more contemporary gender role attitudes. A mediational chain was evident, wherein the interaction of maternal PPD and fathers' gender role attitudes predicted paternal engagement, and lower paternal engagement subsequently predicted more child behavior problems at 12 months, which predicted more child behavior problems at 18 months. CONCLUSIONS: Results suggest the effects of maternal PPD on children's behavior problems may operate via paternal engagement, which is affected by fathers' traditional gender role attitudes. The study highlights the importance of examining fathering and children's behavior using a cultural-contextual lens among underrepresented ethnic minority families.