Introduction: The positive effects of exercise training on some physiological indices of hypothalamic-pituitary-adrenal axis function may improve the brain and peripheral devices, and as improvement of depression. The purpose of this study was to determine the effect of eight weeks of water aerobics on levels of beta-endorphin of women with moderate and mild depression. Materials and Methods: In this experimental study 18 nonathletic females in Yazd Khatam Alanbiya Clinic with mild depression (n=9) moderate (n=9) which had been determined by the Beck Inventory were divided into two groups. Before and after eight weeks of water aerobics, blood samples were taken to measure the Beta-endorphin. Data were analyzed using descriptive and inferential statistics such as t-tests and person’s correlation. Results: The mean and standard deviation of Beta-endorphin before and after the 8-week water aerobics in the mild depression group and moderate depression were 303 ± 374, 298 ± 401 and 73±240, 76±247 respectively. The results also indicated that 8 weeks of water aerobics did not have a significant effect on plasma β-endorphin levels in the depressed patients (p>0.05). Conclusion: Results showed an increase in the beta endorphin serum of women with mild and moderate depression, but this increase was not significant.