Based on social exchange theory, this study proposes a research model to understand the influence of online social support on customer citizenship behaviors by an empirical study. The results show that: online social support includes the dimension of informational support and emotional support; customer citizenship behaviors include the dimensions of recommendations, providing feedback, and helping other customers; online social support positively influences customer citizenship behaviors through relationship quality. In addition, relationship quality fully mediates the relationship between informational support and recommendations, and emotional support and providing feedback; relationship quality partially mediates the relationship between informational support and providing feedback, informational support and helping other customers, emotional support and recommendations, and emotional support and helping other customers.