ABSTRACTIntroduction: The key step in changing health behavior is understanding why users continue to use fitness apps. Therefore, we intend to investigate the users’ intention to continue using social fitness-tracking apps. Materials and Methods: We identify two major forces driving continuous behavior. Expectation confirmation is the internal driving force and social comparison is the external driving force. A survey was conducted to test this proposed research model. We obtained 211 valid questionnaires. Results: Our results indicate that activity amount ranking (p < 0.001) and activity frequency ranking (p < 0.001) positively affect confirmation and that confirmation (p < 0.001) also positively affects the continuous intention of individuals using fitness-tracking apps. In addition, the impact of activity amount ranking and activity frequency ranking on continuous intention is moderated by expectation confirmation. Meanwhile, as the upward comparison tendency increases, the positive effect of confirmation on continuous intention decreases (p < 0.001). Conclusions: Social rank expectation and confirmation are the primary driving forces of continuous intention in individuals using fitness-tracking apps. Social rank is a meaningful and straightforward measurement individuals can use to evaluate their activity performance. An upward comparison tendency weakens the effect of confirmation on continuous intention.