Background: The purpose of this study is to examine the effect of a walking exercise on body water among sedentary obese and thin women. Methods: Forty young untrained girls between the age of 20 and 25 years (obese, BMI>30: N=20 and thin, BMI <20: N=20) volunteered to participate in this study. Participants were randomly assigned to two exercise (obese=10, thin=10) and two control (obese=10, thin=10) groups matched for BMI. DXA was used to measure each subject′s body water, percentage body fat and lean mass. Serum estrogen level by radioimmunoassay (RIA) was assessed. Each walking session was 30 min long at intensity corresponding to 50-75% of maximal age adjusted heart rate and 3 days per week for 2 months. Results: Percent body fat and lean mass were affected positively by exercise programme (p< 0.001). Significant change was observed in serum estrogen and body water in both exercise groups (p<0.05). Conclusion: This study demonstrated that 30 minutes walking exercise improved adaptation of body fluids in both obese and thin sedentary women.