The primary purpose of this study was to contrast the effects of two short-duration exercises on mood changes. A secondary goal was to examine the relationship between pre-exercise and post-exercise mood states. The subjects were 15 healthy male graduate students. They were involved in a within-subject design in which each individual completed two trials of running on a treadmill, one trial for 10 minutes and the other for 15 minutes. The Mood Checklist Short-form 1 (MCL-S1) used in the present study represents the participants' mood states before, during, and after exercise. This questionnaire has three sub-scales measuring (a) pleasantness, (b) relaxation, and (c) anxiety. Participants ran on a treadmill for the assigned time at a self-selected intensity after being told to run at a rate that felt good and was not painful. ANOVA results showed that both of the short bouts of exercise affected the subjects' mood, because the main effect of time spent exercising was observed in all sub-scales of the MCL-S1 and there were no significant differences in trial-by-time interaction. In addition to these results, there was a significant correlation between the two trial lengths in the amount of pleasantness and the amount of anxiety felt at post-exercise. There were moderate differences in the effect size (ES) for pre- and post-exercise pleasantness and anxiety levels. These results revealed similar patterns of change. It seems reasonable to conclude, based on this study, that exercise between 10 and 15 minutes results in similar psychological benefits for the person exercising.