Abstract: Hongkong oyster is a king of marine shellfish in southern China with high yield and low value.In order to increase its added value, this study took Hongkong oyster as raw materials, through enzymatic hydrolysis combined with cell experiment of hydrolysates and its ultrafiltration fractions analyzed the composition characteristics and immune activity evaluation.The results indicated that the oyster hydrolysates and its ultrafiltration fractions molecular weight distribution were mainly concentrated in the < 2.5 k Da, and the content was 53.00% ⁸5.00%, and the complete amino acid composition.The oyster hydrolysates in vitro can promote the immune function of mice spleen lymphocytes and peritoneal macrophages.Further study on the immune activity of oyster hydrolysates, in the concentration range of 0.25 ~ 4.0 mg/m L, in vitro assays of cellular immune captivity of different ultrafiltration products ( > 10, 10 ~ 5, 5 ~ 2.5 k Da and < 2.5 k Da) hasa certain concentration correlation, and < 2.5 k Da and5².5 k Da components have significant immunomodulatory effects. < 2.5 k Da and 5 ~ 2.5 k Da afractions of each oyster hydrolysates ultrafiltration components may be used as an object for further study.