To explore the effects and molecular mechanism of icariin on the vascular function of mice with type 1 diabetes induced by alloxan, type 1 diabetic mice model was established by intraperitoneal injection with 200 mg/kg alloxan.After oral administration with icariin (60, 120 mg/kg) daily for 2 weeks, blood glucose, body weight, food intake and water intake were detected.To evaluate the impact of icariin on the function of isolated vascular ring contraction and relaxation, thoracic aortas of mice were removed and the Ach-induced vascular ring relaxation, Phe-induced vascular ring contraction, SNP-induced vascular ring relaxation and KCl-induced vascular ring contraction response were detected.To further confirm the mechanism of icariin to improve vascular function, human umbilical vein endothelial cells (HUVECs) were induced by high glucose (HG) in vitro.Western blot was used to detect the effect of icariin on eNOS, p-eNOS, p38 MAPK and p-p38 MAPK expressions in HG-induced human umbilical vein endothelial cells (HUVECs).The results indicated that icariin significantly ameliorated the weight loss and dampened the increase in water intake of the diabetic mice.Meanwhile, icariin had a certain ameliorative effect on blood glucose and food intake without significant difference.The results of isolated thoracic aortas vascular rings contraction and vasodilation function indicated that icariin significantly improved Phe-induced vascular contraction and Ach‐induced vascular relaxation.Meanwhile, icariin had a certain ameliorative effect on KCl-induced vascular contraction response without significant difference.However, no significant change was observed on endothelium‐independent vascular rings relaxation response induced by SNP after treatment with icariin.Results of Western blot showed that icariin inhibited the expression of p-p38 MAPK and induced expression of p-eNOS in the high glucose-induced HUVECs cell model.Therefore, icariin may attenuate alloxan-induced type 1 diabetic mice vascular diastolic function by inhibiting expression of p-p38 MAPK and inducing expression of p-eNOS.