A clinical assay of Olea europaea L. aqueous extract was carried on two groups of patients suffering with essential hypertension. 12 patients consulting for the first time, 18 patients with antihypertensive treatment. Treatment based on Olea europeae L. leaf aqueous extract was given (400 ng x 4/24 h) during 3 months, after 15 days treatment based on placebo. We note for all patients a statistically significant decrease of blood pressure (p < 0.001), we didn't find any modification of biological parameters excepted a significant little decrease of glycemia and calcemia p < 0.01 and p < 0.01 respectively. We didn't find any side effect in the two groups.