ObjectiveThis study investigated how new mothers' perceptions of maternal grandmothers' gatekeeping behaviors and perceptions of fathers' parenting competence are associated with maternal gatekeeping behaviors.BackgroundIn the development of coparenting relationships at the transition to parenthood, the roles of extended family members, although important, have received little research attention. Grandmothers' gatekeeping may serve as a reference for maternal gatekeeping behaviors, but its role depends on mothers' own perceptions of fathers' parenting competence.MethodMothers from 172 dual‐earner, different‐gender couples reported their own mothers' gatekeeping behaviors and their own perceptions of fathers' parenting competence at 3 months postpartum. Maternal gatekeeping behaviors toward fathers were reported by mothers at both 3 and 9 months postpartum.ResultsWhen mothers perceived that maternal grandmothers engaged in higher levels of gatekeeping behaviors, mothers engaged in more gate‐opening behaviors but only when mothers perceived fathers as highly competent. There were no significant associations between mothers' perceptions of grandmothers' gatekeeping and maternal gate‐closing behaviors.ConclusionAdult mothers, who likely have developed their own sets of ideas about parenting, are still susceptible to support and criticism from their own mothers.ImplicationsPractitioners would do well to encourage expectant and new parents to consider the role of extended family in the development of their coparenting relationships and to develop plans for support‐seeking, boundary management, and negotiation of conflicts. To help reduce maternal gate‐closing and enhance maternal gate‐opening behaviors, practitioners could support fathers' development of parenting skills and help mothers develop awareness of fathers' skills.