Antioxidants that derived from food have a powerful potential effects on several diseases associated with oxidative stress. The goal of our work was to evaluate the role of quercetin on endothelial dysfunction and asymmetrical dimethylarginine (ADMA) levels in experimental diabetes, rats were divided into four groups including control, quercetin, diabetic and treated groups. Diabetic rats were treated with quercetin; blood glucose and plasma insulin were estimated. Liver superoxide dismutase (SOD), reduced glutathione (GSH) and plasma nitric oxide (NO) were measured. ADMA was estimated by reversed phase HPLC. Our results revealed an increase in insulin resistance and ADMA concomitant with a decrease in plasma nitric oxide, liver superoxide dismutase and reduced glutathione activities while treatment with quercetin significantly ameliorated these parameters in treated group compared to diabetic group. Also a negative correlation between ADMA and NO was found accompanied with a positive correlation between ADMA and insulin resistance. The important role of quercetin in attenuating endothelial dysfunction and elevated ADMA levels provides strong evidence that it may be a promising antidiabetic and protective natural product against cardiovascular complications related to diabetes.