Objective: The first aim of this study was to examine changes in freshman college students' health-enhancing physical activity (PA) and body composition across the first semester. Secondly, this study aimed to explore the role of socio-ecological variables on these processes. Methods: A sample of 166 participants (108 females, 58 males, M[subscript age] = 18.14[0.96]) completed self-report pre-and posttest data on vigorous PA (VPA), moderate-to-vigorous PA (MVPA), and body mass index (BMI). Results: The results showed a statistically significant increase in BMI, but no statistically significant changes in VPA or MVPA. The findings revealed that our socio-ecological model predicted 0.71, 0.39, and 0.92 percent of the end of the year VPA, MVPA, and BMI, respectively. The findings highlighted the positive role of peer support, positive motivation, and university's Recreational Services on measured healthy behaviors. Conclusions: These findings suggest a need to increase college students' VPA.