The purpose of this study was to investigate the effects of aquatic stabilization exercise on lumbar muscle activity, static balance and the body mass index (BMI) of overweight adults. 20 subjects with excess weight were divided into two groups: the aquatic group (n= 10) and the control group (n = 10). The aquatic group conducted aquatic stabilization exercises for 30 minutes, 3 times a week for a duration of 6 weeks. In order to investigate the changes to low back muscle activity, erector spinae, rectus abdominalis, external oblique, and internal oblique muscle activity were measured using surface electromyogram. Sway length and sway speed were measured using balance measuring equipment. While the BMIs of the subjects were measured using a body composition analyzer. The measurements were taken at the start of the study, after 2 weeks, after 4 weeks and after 6 weeks. As result of changes to low back muscle activity, erector spinae, external oblique, and internal oblique muscle activity showed significant improvement over the control group after 2 weeks of exercise. After 4 weeks, the muscle activity of rectus abdominalis had significantly improved from that of the control group. Additionally, the aquatic group showed a significant decrease in sway length and sway speed (p< 0.05) after 4 weeks. A significant difference in the decrease of BMI (p< 0.05) between the groups was detected after 6 weeks.