Abstract: Objective To observe the effect of oral magnesium supplementation on insulin receptor affinity in elderly rats with type 2 diabetes mellitus（DM）. Methods After oral magnesium was supplemented to type 2 DM model of elderly rats,liver cell insulin receptor affinity was assayed,serum levels of fasting glucose,insulin and magnesium,and stable glucose infusion rate were measured with the euglycaemic-hyperinsulinaemic clamp technique. Results The constant of high and low affinity insulin receptor banding was significantly higher while the capacity of high and low affinity insulin receptor banding was significantly lower in high dose magnesium（2g/kg） supplementation group than in DM control group（4.83±0.09）×108/mol Pr vs（1.12±0.17）×106/mol Pr,（4.46±0.16）×1010/mg Pr vs（8.32±0.27）×1013/mg Pr,P＜0.05).The serum levels of fasting glucose and insulin,and insulin sensitivity index（HOMA-IR） were significantly lower while the stable glucose infusion rate was significantly higher in high dose magnesium（2g/kg） supplementation group than in DM control group. Conclusion Oral magnesium supplementation can improve the insulin receptor affinity and reduce the insulin resistance in elderly rats with type 2 DM.