Abstract: Oyster was taken as the research object,under the condition of the same degree of hydrolysis,the effects of trypsin,animal protease,alkaline protease,neutral protease and flavor protease on the sensory,peptide molecular weight and free amino acid of oyster hydrolysate were studied. The results showed that the five hydrolysates all had strong umami flavor. The whole sensory evaluation of alkaline protease hydrolysates was the best among the five hydrolysates. The percentage of peptide area with molecular weight less than 5 kDa was trypsin(74.99%),animal protease(73.44%),neutral protease(71.53%),alkaline protease(68.46%)and flavor protease(58.77%). The percentage of free amino acids was the highest in glutamic acid and the lowest in histidine. The total content of free amino acids from high to low were trypsin(22.816 mg/g),neutral protease(20.775 mg/g),flavor protease(20.530 mg/g),animal protease(16.287 mg/g)and alkaline protease(16.232 mg/g). The number of free amino acids with a TAV greater than 1 in trypsin,animal protease,alkaline protease,neutral protease and flavor protease was 10,8,8,9 and 11 respectively. Among the five hydrolysates,the amino acid with the largest TVA value was glutamic acid.