Most studies indicate that psychological capital had a positive effect on organizational citizenship behavior. However, the effect of psychological capital on organizational citizenship behavior has not yet been fully understood. Based on the Conservation of resources theory, this study examines the effect of psychological capital on well-being and organizational citizenship behavior. Using structured questionnaires, this study collected data from a diverse sample of 273 full-time Taiwanese employees. Results showed that psychological capital and well-being have a positive effect on organizational citizenship behavior, and well-being has a positive effect on organizational citizenship behavior. Moreover, well-being mediated the relationship between psychological capital and organizational citizenship behavior. Finally, the theoretical and practical implications of the findings were discussed.