The purpose of this study was to examine the effects of daily exercise of varying duration on the body composition, weight, and feed intake of mature Swiss albino mice. Fifty-four male mice were equally divided into a control group and five exercise groups (n = 9) performing 20, 40, 60, 120, and 240 min of daily exercise on a treadmill (7.2 m/min). Feed intake and body weight were measured weekly for 10 wk. At the completion of the study the mice were killed and the animal carcasses were chemically analyzed for fat, dry matter, and protein content. The results of this study demonstrate no differences in the body weight among groups (P less than 0.97) with all groups gaining 4.5–5.8 g during the 10-wk period. However, fat content decreased significantly from 15.7% in the control to 12.0% in the 120- and 240-min exercise groups (P less than 0.05). In contrast, protein content showed an insignificant rising trend from 13.0 to 14.6% with increasing duration of exercise. Feed intake showed a nonsignificant drop during the 20-min exercise treatment and remained unchanged among groups. These data show a slight but variable appetite-suppressing effect of light exercise in mice accompanied by favorable body composition changes even in the absence of differences in body weight. These findings suggest the mouse to be an acceptable experimental model for body composition and exercise studies.