Background Endothelial function of coronary artery was impaired by abnormal glucose metabolism.LDL-C has been shown to inhibit endothelial function, and promote the development of atherosclerosis.HDL-C may exert beneficial effect on endothelial function.However, the effect of LDL-C and HDL-C on coronary endothelial function remains uncertain under the pathophysiological condition of type 2 DM.This study sought to evaluate the association between coronary artery endothelial function and the plasma levels of Low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C) in patients with type 2 diabetes mellitus (DM).