Abstract: Objective To observe the effect of aging on fat ectopic deposition in non-adipose tissues of Wistar rats. Methods Thirty healthy male Wistar rats were divided into 4-month old group（youth group,n=15） and 24-month old group（aged group,n=15）.Two months after they were fed with normal chow,their body weight and intra-abdominal fat weight were observed,levels of their free blood glucose（FBG）,insulin（INS）,triglyceride（TG）,cholesterol（TC） and free fatty acid（FFA） were measured,while their insulin sensitivity was detected by the euglycaemic-hyperinsulinaemic clamp technique.Fat level in frozen liver,muscle and pancreatic tissue sections was measured by computer software with oil red O staining at the end of experiment. Results The body weight was significantly higher in aged group than in young group（（730.9±9.57）g vs（495.6±7.53）g,P＜0.01）).The fat content in liver,perirenal and epididymis tissues,and the TG,TC and FFA levels were significantly higher in aged group than in young group（P＜0.05）.The INS level was significantly higher in aged group than in young group（（2.37±0.06）ng/ml vs（0.59±0.32）ng/ml,P＜0.01）).No significant difference was observed in FBG between the two groups（P＞0.05）.Euglycaemic-hyperinsulinaemic clamp test showed that the glucose infusion speed was significantly higher while the HOMA-IR was significantly lower in young group than in aged group（（26.07±2.80）mg/（kg·min） vs（10.79±0.71）mg/（kg·min）,（3.07±0.75） vs（13.15±l.56）,P＜0.05）),but no significant difference was observed in HOMA-β between the two groups.Oil red O staining displayed that the number of fat drops in liver and muscles was significantly greater in aged group than in young group（P＜0.01）,but no fat drop was found in the two groups by panreatoscopy.Grey scale analysis revealed that the grey scale value for liver adipose tissue staining and muscles fat tissue staining was significantly lower in aged group than in young group（（116.60±4.56） vs（175.48±3.02）,（121.70±4.60） vs（150.65±3.60）,P＜0.05）),but no significant difference was observed in the grey scale value for pancreatic adipose tissue staining between the two groups. Conclusion Fat deposition in liver and muscles of aged rats is resistant to insulin at a certain extent.