College students commonly rate stress as the number one health problem with which they deal with on a daily basis. Aerobic exercise is often promoted as an effective tool for stress management and overall improved mental health. Less understood is the utility of exercise intensity as a means to reduce perceived levels of stress and subsequently improve mood. PURPOSE: to investigate the acute effects that the intensity of aerobic exercise has on positive and negative affect. METHODS: College students (n=28) were assessed for affect via the Positive and Negative Affect Schedule (PANAS) questionnaire. In a crossover study, students performed two cycle ergometer protocols 48 hours apart - 1) moderate-intensity at 65% of peak power output for 20-min and 2) vigorous-intensity at 85% of peak power output, performed in a 1-min-on, 1-min-off interval format for 20-min. After the conclusion of the exercise session, the students were assessed via the PANAS a second time, allowing for pre/post analysis. RESULTS: Initial analyses indicated no interaction effect (time x condition) for either positive affect (p=0.065) or negative affect (p=0.064). Positive affect scores increased from pre to post in both conditions (65%: p<0.001, d=1.2; 85%: p<0.001, d=1.2). Negative affect scores decreased from pre to post in both conditions (65%: p<0.001, d=0.92; 85%: p<0.001, d=0.89). CONCLUSIONS: The results of this study found that an acute 20-min bout of cycling at both 65% and 85% of peak power led to large improvements in positive affect (18.8%, 27.4%) and large decreases in negative affect (23.5%, 17.6%). Moderate and vigorous-intensity aerobic exercise were equally effective in improving mood in this college population.