Abstract: Objective:To observe the changes of Ghrelin level in serum and hypothalamus of high-diet induced obesity rats after 6-week swimming exercise, and to investigate the association of Ghrelin with obesity and metabolic syndrome. Methods:Fifty SD rats were randomly divided into normal diet group(NC, n=10) and high fat diet group(HD, n=40). Obesity models(n=20) were established from the HD group,and equally assigned to obesity group(OB) and swimming exercise group(SWI). The SWI group received standard swimming exercise 1 hour/day,5 day/week for 6 weeks,and the other two groups were given distilled water. Their body weight(BW), fasting plasma glucose(FPG),triglyceride(TG),total cholesterol(TCH),fasting insulin(FINS),HOMA index and fasting Ghrelin were measured 6 weeks before and after the intervene; the Ghrelin expression in the hypothalamus was detected by immunohistochemistry. Results:The BW,FPG,TG,TCH,FINS levels and HOMA-IR in the OB group and in the SWI group were increased and the Ghrelin level was decreased in contrast to the NC group before the intervene(P0.01);the BW,FPG,TG,TCH,FINS levels and HOMA-IR in the SWI group were decreased and the Ghrelin level was increased compared to that in the OB group(P0. 01) after the intervene. Immunohistochemistry results showed that the Ghrelin expression level was increased in the hypothalamus of the OB group but was down-regulated in the SWI group(P0. 05). Conclusions:Swimming exercise can improve the insulin resistance and reduce the weight and Ghrelin levels in obesity rats.