Danzhi jiangtang capsule (DJC) is mainly used to treat type 2 diabetes mellitus and vascular complication. Our aim was to investigate whether the protective effects of DJC by oral administration on high-fat diet (HFD) and palmitic acid-induced damages of endothelial cells are related to oxidative stress and endoplasmic reticulum (ER) stress. Male Sprague-Dawley rats were randomly divided into standard chow diet (SCD), HFD, HFD plus DJC-low dose (HFD + DJCL) and HFD plus DJC-high dose treatment groups (HFD + DJCH). The latter three groups were given HFD feeding for three months, then the HFD + DJCL and HFD + DJCH rats were treated with DJC (500 and 1000 mg/kg/day) via gavage for another two months respectively. Endothelium-dependent relaxations induced by acetylcholine were observed in isolated rat thoracic aortic ring preparation. Malondialdehyde (MDA), total-antioxidant capacity (T-AOC), superoxide dismutase (SOD), interleukin 1β (IL-1β), tumour necrosis factor α (TNFα), free fatty acids (FFA), endothelin-1 (ET-1) and nitric oxide (NO) levels in serum were assayed. The pathological changes, protein expression of endothelial NO synthase (eNOS), phosphorylated eNOS (p-eNOS) and ER stress-related genes in the thoracic aorta were measured. Human umbilical vein endothelial cells (HUVEC) were treated with serum-medicated DJC and then with palmitic acid to detect the reactive oxygen species (ROS) levels and C/EBP homologous protein (CHOP) distribution, expression of p-eNOS and ER stress-related genes. DJC therapy exhibited a potent antioxidant activity and effectively prevented the endothelial dysfunction (ED) manifested by promoting p-eNOS expression and enhancing NO release, decreasing lipid deposition (Oil-red O staining, CPT1b and ACC) and inflammation (IL-1β, TNFα, CD68 and p-JNK), alleviating oxidative and ER stress, and decreasing the apoptosis of endothelial cells (TUNEL, BCL-2 and BAX) induced by HFD and palmitic acid respectively. These findings suggest that the administration of DJC had endothelial protective effects against HFD-induced ED, inflammation and apoptosis by alleviating lipid deposition, oxidative and ER stress.