When studying factors that may heighten risk for relational aggression in youth, it is important to consider characteristics of both the individual and their environment. This research examined the associations between parental psychological control and reactive and proactive relational aggression in emerging adults in college. Given that sympathetic nervous system (SNS) activation may underlie differences between reactive and proactive aggression and has been shown to moderate the effects of parenting on youth development, the moderating role of SNS reactivity [indexed by skin conductance level reactivity (SCLR)] was also examined. Emerging adults (N = 180; 77.2 % female) self-reported on perceptions of parental psychological control and reactive and proactive relational aggression. SCLR was assessed in response to an interpersonal laboratory challenge task. Parental psychological control was positively associated with reactive relational aggression only for emerging adults who exhibited high SCLR. Parental psychological control was positively associated with proactive relational aggression only among emerging adults who showed low SCLR. This study extends previous research on parenting and aggression and suggests that parental psychological control is differentially associated with reactive versus proactive relational aggression, depending on emerging adults’ SCLR to interpersonal stress.