Abstract: Despite the popularity of gamified geosocial fitness applications, there are only a few empirical studies examining their effectiveness in promoting physical activity. This study proposes co-presence, which combines spatial and social attributes of presence experience, as a theoretical construct that captures the essence of user engagement with the gamified geosocial mobile fitness applications. Co-presence in this study is defined as a sense of being with competitors (i.e., co-presence with competitors) and/or cooperators (i.e., co-presence with cooperators) in a physically and/or electronically shared space. The current study discusses and examines (1) potential determinants of co-presence and (2) how the two types of co-presence are related to perceived social support, exercise self-efficacy, and exercise adherence. Analyses of data collected through an online survey among gamified geosocial fitness application users showed that a perceived geographical proximity to other social entities with whom users interact through mobile health applications is positively related to both types of co-presence. The results also demonstrated that co-presence with competitors is positively related to exercise self-efficacy and exercise adherence; whereas co-presence with cooperators is only positively related to perceived social support. Implications and direction for future studies are discussed.