Aim To evaluate the effect of oral folic acid on endothelial function in elderly hypertensive patients. Methods Fourty-two elderly patients with mild essential hypertension were divided with randomized principle into two groups: folic acid administrative group(n=22) and control group(n=20).Flow-medicated dilatation(endothelium dependent) and nitroglycerin-induced dilatation(endothelium independent) using high-resolution ultrasound were measured before and 12 weeks after treatment. Results The difference of baseline diameter(D_0) in the two groups were not statistically significant before and after treatment.Flow-mediated dilatation of patients with folic acid administration group(11.59%±4.79%) was improved significantly compared with that of pretherapy(7.15%±3.20%) and control group(8.14%±3.01%)(p<0.05).Endothelium-independent dilation(19.73%±5.80%) also was improved significantly compared with that of pretherapy(16.69%±4.75%) and control group(17.55%±6.05%)(p<0.05). Conclusion Folic acid administration improves arterial endothelial function in elderly hypertensive patients.