In exercise psychology, mental health is often studied as symptoms of mental illness, and rarely as a positive psychological construct. As such, the relationship between positive mental health and physical activity is not understood. Specifically, flourishing is a self-reported measure of well-being and a positive mental health indicator. The purpose of this study was to explore the directional relationships between flourishing and moderate-to-vigorous physical activity (MVPA) in first year university students. The Broaden and Build model would suggest that flourishing would predict MVPA, whereas emotion-focused models would suggest that MVPA would predict flourishing. Students (N = 231, 68% female) completed surveys in September (T1) and March (T2) of their first year. Preliminary analyses demonstrated no significant change in MVPA, t(230)=.25, p=.8, and a significant decrease in flourishing, t(230)=4.24, p<0.001. Males reported significantly more MVPA at T1 compared to females, with no other sex differences. In the main analyses, an autoregressive path model was estimated: ?2(2)=.35, p=.83, RMSEA=0.0 (90% CI=0-.07), CFI=1, SRMR=.01. In this model, the cross-legged paths were significant, demonstrating T1 MVPA was related to T2 flourishing (ß=.17), and T1 flourishing was related to T2 MVPA (ß=.12), while also estimating the significant stable paths between T1 and T2 MVPA (ß=.42) and flourishing (ß=.69), respectively, and controlling for sex. The findings support that both flourishing and physical activity should be of focus when designing programs and interventions for first-year university students to enhance their mental and physical well-being.