Background <p>Paternal postpartum depression (PPPD) remains underrecognized globally, despite prevalence estimates comparable to maternal depression. This study investigated whether a childbirth and parenting booklet distributed to expectant fathers during the prenatal period could reduce the risk of PPPD.</p> Methods <p>We performed a parallel-group, randomized controlled trial conducted in an obstetrics clinic in Japan. We recruited expecting fathers and their pregnant partners at 28–32 weeks gestation. In total, the intervention and control groups comprised 236 and 234 couples, respectively. The intervention comprised of a childbirth and parenting booklet that was distributed to the fathers by postal mail at 32 to 34 weeks gestation. The primary outcome was the incidence of paternal depression at 1 or 3 months after delivery. The secondary outcomes measured in this study included various indicators related to participants and childcare.</p> Results <p>At follow-up, signs of depression were observed in 7.2% of fathers in the intervention group and 9.8% in the control group (<i>p</i> = 0.40). Multivariable logistic regression analysis showed a reduced, but non-significant risk of PPPD (odds ratio = 0.70, 95% confidence interval = 0.34–1.42). There were no significant associations in secondary outcomes between the intervention and control group.</p> Conclusions <p>Distributing a booklet alone may not be sufficient to reduce the risk of PPPD. More personalized, interactive, or accessible interventions may be necessary to support paternal mental health during the perinatal period.</p> Trial registration <p>UMIN000021475 (15/03/2016).</p>