Objective: To observ effect of Huangqi Gegen decoction on insulin resistance(IR) and gene expression of peroxisome proliferator-activated receptor-γ(PPAR-γ) in type 2 diabetes mellitus(T2DM) rats. Method: Male Wistar rats were randomly divided into nomal group,model proup.The rats of normal group were fed with common food while the others with high calorie food for 4 weeks and injected with low dose of STZ. The level of fasting blood glucose(FBG) and 2 hours blood glucose(2 h BG) of glucose load were measured by routin method in rats with hyperlipemia after one week. The rats with nomal FBG level and 2 hBG level ≥7.8 mmol·L^-1 were as model rats. The model rats were randomly divided into model group, rosiglitazone group, and high, middle, low dose of Huangqi Gegen decoction groups(8,4,2 g·kg^-1). After intervention by drugs for 8 weeks, FBG, fasting insulin (FINS), leptin, TNF-α level of all rats were measured and insulin sensitivity index(ISI), insulin resistance index(HOMA-IR) were calculated accordingly. At the end of experimental treatment, the total mRNA of greater omental adipose tissues were extracted and the genic fragments of PPAR-γ were amplificated in order to detect their expression levels. Result: Huangqi Gegen decoction could enhance ISI, reduce HOMA-IR, plasm Leptin and TNF-α level in model rats, and increase the expression of PPAR-γ mRNA. Conclution: Huangqi Gegen decoction can improve IR condition of the model rats and its mechanism is probably related to its effect of reducing plasm leptin and TNF-α level,enhancing the genic expressional level of PPAR-γ.