The hypotensive effect of an aqueous extract of Fraxinus excelsior L. was investigated in both normotensive (WKY) and spontaneously hypertensive rats (SHR). Daily oral administration of Fraxinus excelsior (20 mg/kg) aqueous extract for 3 weeks produced a significant decrease in systolic blood pressure (SBP) with variation coefficient (Δ%) of 13.5% in SHR ( p < 0.01) and 9% in WKY rats ( p < 0.05). The aqueous extract of Fraxinus excelsior significantly enhanced the urination in both SHR ( p < 0.05 compared to control) and WKY ( p < 0.05 compared to control). Irbesartan (Avapro ®), an angiotensin II antagonist, was used as reference drug. Furthermore, oral administration of aqueous Fraxinus excelsior extract at a dose of 20 mg/kg produced a significant increase in urinary excretion of sodium ( p < 0.01 compared to control), potassium ( p < 0.001 compared to control) and chlorides ( p < 0.01) in SHR rats. In normal rats, the aqueous Fraxinus excelsior extract administration induced a significant increase of the urinary elimination of sodium ( p < 0.05 compared to control), chlorides ( p < 0.01 compared to control) and potassium ( p < 0.01 versus control). While there were no significant changes in heart rate (HR) after Fraxinus excelsior treatment in both SHR and WKY rats, glomerular filtration rate (GFR) showed a significant increase in SH rats ( p < 0.001) after Fraxinus excelsior treatment. These results suggest that oral administration of aqueous extract of Fraxinus excelsior exhibited hypotensive and diuretic actions.