Based on self-determination theory (SDT), the main goal of this study is to analyze dispositional flow and social physique anxiety (SPA) that could be predicted by gender, BMI and motivational regulations and to examine motivational regulations, dispositional flow and SPA of college students in terms of stage of change for exercise. Participants (n = 612) completed questionnaires measuring exercise motivation, exercise stages of change, dispositional flow and SPA. Multiple regression analyses revealed that gender, intrinsic and introjected regulation were positive predictors, BMI and external regulation were negative predictors of the flow experience. On the other hand, BMI and external regulation were positive predictors and gender was negative predictor of SPA. Participants at early stages (at preparation and action) have less intrinsic and introjected regulation and more amotivation scores than those at maintenance stage of change for exercise. Additionally, exercisers at maintenance stage displayed significantly less SPA and showed greater tendency to experience flow than preparation and action stages. The results of this study further the understanding of the motivational process and somehow showed that gender and BMI explain SPA and dispositional flow in college students within an exercise context. The other significant results of this piece is to enable the importance of promoting intrinsic motivation, introjected regulation and flow experience as well as reducing perceiving SPA of exercisers in order to foster their exercise behaviours.