OBJECTIVE Parental posttraumatic stress disorder (PTSD) increases children's risk for emotional and behavioral problems. We examined parenting stress and parenting behavior quality as mediators of the relation between maternal PTSD and problematic child behaviors in a sample at high risk for trauma exposure. We also examined whether child sex moderated this association. METHODS Participants were 141 African American mother-child dyads (children aged 8-12). Mothers reported PTSD severity, parenting stress, and child behavior (externalizing, internalizing, and emotional self-control). Parenting behavior quality (accounting for factors including parental warmth and engagement) was assessed from an observational parent-child interaction task. RESULTS Parenting stress, but not observed parenting behavior quality, mediated the relation between maternal PTSD severity and child behaviors. Child sex moderated this association, such that the effect was stronger for girls. CONCLUSIONS Maternal PTSD may be associated with negative child behavior outcomes, and this relation appears to be mediated by increased parenting stress. Stress-reducing interventions for parents with PTSD could improve child outcomes, especially for girls. (PsycInfo Database Record (c) 2022 APA, all rights reserved).