Hipertension is one the key risk factors of cardiovascular disease. Treatment of hypertension is currently being developed, one of the mecanism is inhibition of ACE (Angiotensin Converting Enzyme). This research was aimed to test of in vitro the inhibitory activity of ACE using ACE kit-WST, determining of total phenolic compound, and total flavonoid from watercress herb ethanol extract. The result showed that watercress herb extract had ACE inhibitory activity with IC₅₀ value 19,05 μg/mL. Watercress herb extract showed the total phenolic compound in amount of 5,71 mg GAE/g extract and showed total flavonoid compound in amount of 4,44 mg QE/g extract.