ABSTRACTBackgroundFathers are key influencers of complementary feeding practices, but few studies in low- and middle-income countries have measured the effects of complementary feeding social and behavior change communication (SBCC) targeted at both fathers and mothers.ObjectivesThe aims of this study were to measure the effects of an SBCC intervention on children's dietary diversity (primary outcome) and other complementary feeding indicators, fathers’ and mothers’ complementary feeding knowledge, and fathers’ support for complementary feeding (secondary outcomes).MethodsThe 12-mo intervention in Kaduna State, Nigeria, engaged parents through community meetings, religious services, home visits from community health extension workers (CHEWs), mobile phone messages (fathers only), and mass media. Cross-sectional population-based surveys of cohabiting fathers and mothers with a child aged 6–23 mo were conducted, and regression models were used to compare results at baseline (n = 497) and endline (n = 495).ResultsChildren's minimum dietary diversity did not change from baseline to endline (62% to 65%, P = 0.441). Children's consumption of fish (36% to 44%, P = 0.012) and eggs (8% to 20%, P = 0.004) and minimum meal frequency (58% to 73%, P < 0.001) increased. Fathers’ and mothers’ knowledge of the timing of introduction of different foods and meal frequency improved. Fathers’ support for child feeding by providing money for food increased (79% to 90%, P < 0.001). Fathers’ and mothers’ reported intervention exposure was low (11–26% across types of SBCC). Child feeding outcomes were not associated with fathers’ exposure. Children's odds of both fish and egg consumption increased significantly with mothers’ exposure to community meetings, religious services, home visits, and television spots, and children's odds of minimum meal frequency increased significantly with mothers’ exposure to home visits.ConclusionsA multipronged SBCC intervention improved complementary feeding practices, fathers’ and mothers’ knowledge of complementary feeding, and fathers’ support for complementary feeding, despite low levels of reported exposure, which may have been influenced by coronavirus disease 2019 (COVID-19) disruptions. This trial was registered at ClinicalTrials.gov as NCT04835662.