Abstract: Phascolosoma esculenta water-soluble protein hydrolyzed by pepsin, alkali protease, trypsin, neutral protease, and papain were studied. The hydrolysis condition of pepsin was optimized, with the ACE inhibiting rate as the major indicator, to:pH1.8, 37℃ , E/S 0.3% (w/v) and 4h. Under the optimized condition of pepsin hydrolysis, the IC 50 of hydrolysate was 1.85mg/mL. The activity of ACE inhibitor in vivo was further investigated with spontaneously hypertensive rats (SHR) and results showed that blood pressure start to decrease significantly after 1h of oral administration and the average value of SBP reduced 17mmHg in 8h.