Neighborhood social capital--resources inherent within community networks--has been identified as a potential facilitator of personal well-being. We test hypotheses concerning how neighborhood social capital moderates the influence of parenting strain on mastery (individuals' understanding of their ability to control personal life circumstances) for female primary caregivers of children. First, we test how different forms of neighborhood social capital--social support, social leverage (information exchange), informal social control, and neighborhood organization participation--modify the association between parenting strain and mastery. Second, we test whether such moderation depends on one's access to these forms via neighbor ties. Analyses of Los Angeles Family and Neighborhood Survey data (N = 765) indicate that the negative relationship between parenting strain and mastery worsens as informal social control increases. Social support and informal social control, however, buffer this parenting strain-mastery relationship when caregivers have stronger ties to neighbors. Our findings implicate mechanisms of "negative social capital" and warrant more nuanced considerations of neighborhood social capital's health-promoting potential. (Contains 3 tables and 3 figures.)