To study the effect s of Portulaca oleracea, a Chinese medicinal herb, on insulin resistance in rat s with type 2 diabetes mellitus ( T2DM). Methods: Experimental model of T2DM was established by injection of st reptozotocin (25mg/ kg) and feeding with high calorie forage. The effect s of Portulaca oleracea on oral glucose tolerance, serum levels of insulin, t riglyceride, total cholesterol, highdensity lipoproteins-cholesterol and f ree fatty acids, and insulin sensitivity index were all observed. Results: Portulaca oleracea could reduce the body weight, improve the impaired glucose tolerance and lipid metabolism, decrease serum f ree fatty acids, attenuate hyperinsulinemia and elevate insulin sensitivity. Conclusion: Portulaca oleracea could improve insulin resistance in rat s with T2DM, and the mechanism might be related to it s actions in improving lipid metabolism and decreasing f ree fatty acids.