China is the rich country of fishery on fresh water, the yearly output of fresh water fish is 19.188 million tons, approximately occupy 40% of the total fish output. The main kinds of fish are the silver carp, variegated carp and grass carp. The processing proportion reaches above 75% in developed country, and there is only 30% in our country at present. The fresh water fish are sold primarily fresh with the low price, which has seriously affected the sustainable development of fresh water fishery. Not only have antihypertensive peptides from protein of fresh water fish the advantage of protein, but also they have the character of acid and hot stability as well as the better solubility and unique antihypertensive function, it is easier to digest and absorption than the protein and its amino acid. So It will be the future for deeply processing fresh water fish that fish protein was utilized to prepare for antihypertensive peptides by biological technology. In the paper grass carp protein was hydrolyzed by alcalase and angiotensin Ⅰ-converting enzyme inhibitory activities was assayed by high-performance liquid chromatography for preparing fish antihypertensive peptides. The results indidated that appropriate hydrolysis conditions for alcalase were pH9.0, 50℃, ratio of alcalase to grass carp protein with 48 AU.kg-1, DH34.52%. The analyzing results of components showed that fish antihypertensive peptides made at the same hydrolysis conditions contained 81.26% of soluble N, 72.81% of peptides, 0.12% of fat, 3.54% of water and 9.47% of ash. Angiotensin Ⅰ-converting enzyme inhibitory activities of fish antihypertensive peptides was 70.35%; Its relative molecular weight assayed by size exclusion chromatography distributed from 124 to 10581, and mainly from 124 to 1062. Solubility of antihypertensive peptides from grass carp protein was analyzed during pH3 and pH11, the result showed that its solubility with 96.0% around was steady, and fish antihypertensive peptides could be extensively used in the food. Key words: grass carp; antihypertensive peptides; alcalase; high-performance liquid chromatography; molecular weight; size exclusion chromatography