In the paper,the preparation of bioactive oligopeptides from Porphyra yezoensis proteins in the presence of papain was studied.The ACE inhibitory activity was used as response to optimize the enzymatic conditions.The molecular weight distribution of the hydrolysates was determined by gel filtration chromatography on SephadexG-15 column.The result of which showed that the optimum conditions were pH 7.5,temperature 50℃,substrate concentration 30mg/mL,addition amount of enzyme 600 U/g.Under such conditions,and hydrolyzing for 4 hours,the inhibitory activity of the hydrolysates reached up to 30%,with IC50 value reaching 4.48mg/mL.The hydrolysates of Porphyra yezoensis were then determined by chromatography,the result of which showed that the hydrolysates of antihypertensive activity from Porphyra yezoensis proteins was mainly oligopeptide with molecular weight less than 2000.