Objective: Unmarried mothers have high rates of smoking, including during late pregnancy and after pregnancy, thus increasing their children’s risk for negative health outcomes associated with maternal tobacco use. Few studies have examined whether partners’ smoking exacerbates or attenuates maternal smoking risk. The current study examines how fathers’ behaviors during the third trimester of pregnancy and after pregnancy influence maternal smoking across the first 9 years of a child’s life. Method: Unmarried parents (N = 2,580 pairs) from the Fragile Families and Child Wellbeing Study were measured four times. Paternal and maternal tobacco use during the third trimester was assessed via retrospective report at baseline (the time of the child’s birth). Parents also reported tobacco use 1 year, 5 years, and 9 years later. Paternal supportive behaviors were self-reported at baseline. Results: Paternal tobacco use predicted maternal tobacco use. This association was moderated by paternal supportive behaviors as reported by fathers (b = 0.51, 95% CI [0.22, 0.81], p = .001; adjusted odds ratio = 1.67, 95% CI [1.24, 2.25]). Paternal smoking predicted maternal smoking for fathers who reported both high and low levels of supportive behaviors, but this relationship was stronger for fathers who engaged in the highest levels of support. Conclusions: Unmarried fathers’ smoking had a stronger relationship to maternal smoking during late pregnancy and postpartum when fathers engaged in more support behaviors. The results of this study suggest that targeting fathers’ smoking cessation may help improve the effectiveness of tobacco cessation programs for at-risk unmarried mothers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149446/1/2019 ALBUJA early paternal smoking.pdf