OBJECTIVE： To explore the effects of olmesartan medoxomil on blood pressure variability （BPV） and vascular endothelial function of patients with mild and moderate essential hypertension. METHODS： Sixty patients with mild and moderate essential hypertension were included in study group， and other 60 healthy volunteers were included in control group. Study group was given olmesartan medoxomil 20 mg orally， qd， for 4 weeks， followed by same dose if their SBP≤140 mmHg and DBP＜90 mmHg till 12th weekend； those patients with SBP＞140 mmHg or DBP≥90 mmHg received double dose till 12th weekend. Average blood pressure， BPV， FMD and NMD of study group were measured before and after treatment as well as the changes in serum concentrations of NO and ET， and then compared with control group. RESULTS： Compared with before treatment， average blood pressure， BPV and ET level of study groups were decreased significantly after treatment， serum level of NO was increased significantly， while FMD and NMD were improved significantly， with statistical significance （P＜0.05）； there was no statistical significance， compared with control group （P＞0.05）. There were 3 cases of mild diarrhea and 2 cases of mild dry cough， and they relieved after medication withont speical treatment. CONCLUSIONS： Olmesartan medoxomil can play a good effect on decreasing blood pressure and is tolerable. It can also improve the vascular endothelial function.