PurposeDespite fitness applications (apps) are increasingly downloaded by smartphone users in recent years, the usage behavior after initial adoption often lasts for a short period of time for most users. The purpose of this paper is to explore factors affecting stickiness of fitness app and then indicate how to retain existing users.Design/methodology/approachA research model was developed based on stimulus–organism–response (S-O-R) model. Using the data collected from 231 fitness app users through an online survey, the established model was empirically assessed by structural equation modeling (SEM).FindingsThe results show that human-to-information interaction and human-to-human interaction as environmental stimuli affect individuals' internal state, including social comparison and perception of fitness self-management, which consequently influence the stickiness of fitness apps.Originality/valueThe study provides new insights into the mechanism regarding why users are willing to continuously use fitness apps. Moreover, the understanding of social comparison among users in such process was also deepened.