Objective: The goal of this study was to examine the effect of quality of workplace relationships on the mental health of employed undergraduates, with work-related variables as a potential mechanism. Participants: Participants were 170 employed students (76% female, average age = 19.9) recruited in March 2011. Most worked part-time and had been at their jobs over a year. Methods: Students were recruited from an undergraduate introductory psychology course and completed online surveys about the quality of workplace relationships, mental health (i.e., somatic stress symptoms, depression, anxiety, and life satisfaction), and work-related variables (i.e., job satisfaction, support, turnover and burnout). Results: Students who reported having workplace relationships with co-occurring positivity and negativity had worse self-reported mental health outcomes than students reporting having wholly positive relationships. The relationship between workplace relationship quality and mental health was mediated by negative work-related variables. Conclusions: Workplace relationships--even in part-time employment settings--influence college students' mental health.