Marine Chlorella ellipsoidea protein was hydrolyzed using Protamex, Kojizyme, Neutrase, Flavourzyme, Alcalase, trypsin, alpha-chymotrypsin, pepsin and papain. Alcalase-proteolytic hydrolysate exhibited the highest ACE inhibitory activity among them and was fractionated into three ranges of molecular weight (below 5 kDa, 5-10 kDa and above 10 kDa). The below 5 kDa fraction showed the highest ACE inhibitory activity and was used for subsequent purification steps. During consecutive purification, a potent ACE inhibitory peptide from marine C ellipsoidea, which was composed of 4 amino acids, Val-Glu-Gly-Tyr (MW: 467.2 Da, IC50 value: 128.4 mu M), was isolated. Lineweaver-Burk plots suggest that the peptide purified acts as a competitive inhibitor against ACE and stable against gastrointestinal enzymes of pepsin, trypsin and alpha-chymotrypsin. Furthermore, antihypertensive effect in spontaneously hypertensive rats (SHRs) also revealed that oral administration of purified peptide can decrease systolic blood pressure significantly. The results suggest that marine C ellipsoidea would be an attractive raw material for the manufacture of antihypertensive nutraceutical ingredients. (C) 2012 Elsevier Ltd. All rights reserved.