Aerobic exercise can acutely influence anxious and depressive mood in both clinical and nonclinical populations. However, there are no existing studies that have examined the acute effect of exercise on mood, anxiety, obsessions, and compulsions in patients with OCD. The primary aim of this study was to examine acute changes in these symptoms after engaging in single exercise sessions during a 12-week exercise intervention for 15 (53% female; mean age=41.9 years) patients with OCD. Participants reported reductions in negative mood, anxiety, and OCD symptoms at the end of each exercise session relative to the beginning. Changes in the magnitude of the effect of exercise in reducing negative mood and anxiety remained fairly stable while levels of self-reported obsessions and compulsions decreased over the duration of the intervention. Results of this study point toward the promising effect of exercise for acute symptom reduction in patients with OCD.