Dimensions of negative parenting, including permissive, authoritarian, and psychologically controlling parenting behaviors, are associated with children's engagement in relational aggression. However, some youth may be more strongly influenced by negative parenting than others, and effects may depend on whether aggression is proactive or reactive in function. In a community sample of 236 preadolescent children followed over 1 year, we examined whether children's skin conductance level reactivity (an index of “fight or flight” response) and gender moderated links between parents' self-reported negative parenting behaviors and increases in children's teacher-reported proactive and reactive relational aggression. Findings indicated that negative parenting predicted increases in proactive and reactive relational aggression, and, consistent with differential susceptibility theory, effects often emerged among highly reactive youth. Associations between negative parenting and proactive relational aggression emerged for boys but not girls. Results tentatively suggest that associations between parenting and aggression vary by the function of aggression, children's physiological reactivity to stress, and gender, although results should be interpreted with caution due to high levels of missing data. Implications for theory and intervention are discussed.