Acute moderate-intensity exercise has been demonstrated to improve memory performance. It is less clear, however, whether the duration of acute exercise and body mass index (BMI) may moderate this effect. Thus, the purpose of this experiment was to evaluate the effects of differing exercise durations (20- and 40-minutes) on immediate and long-term memory performance, while considering BMI as a moderating factor in this exercise duration and memory performance relationship. Twenty-three young healthy adults participated in a within-subjects experiment. Participants completed four different experimental visits including either exercising at a moderate intensity (or standing on a treadmill) for 20- or 40-minutes, followed by an immediate free-recall memory assessment and then a delayed 24-hr recall. Acute moderate-intensity exercise improved memory performance, regardless of the duration of exercise. Further, long-term memory performance was greater for individuals with a higher BMI when they engaged in shorter (20 min) exercise compared to longer (40 min) exercise.