This study examined the interaction effect of personality and workplace environment on Organizational Citizenship Behavior (OCB) in young workers, focusing on the mediating effects of Organization-Based Self-Esteem (OBSE). A survey was administered to 380 employees of a variety of companies. Results showed that (1) Leader-Member Exchange (LMX) and Team-Member Exchange (TMX) had positive effects on interpersonal helping behavior through OBSE; (2) LMX had a stronger effect on OBSE than TMX in the low conscientiousness personality group, whereas TMX had a stronger effect on OBSE than LMX in the high conscientiousness personality group; and (3) in the low conscientiousness personality group, the effect of task interdependence on interpersonal helping behavior was stronger than that of OBSE.