Abstract: A 4-week feeding trial was conducted to investigate the effects of chitooligosaccharides (0, 250 mgkg-1, 500 mgkg-1, 750 mgkg-1 and 1 000 mgkg-1) on the growth and non-specific immunization of Litopenaeus vannamei. Results demonstrate that there is significant difference in the total number of hemocytes, growth rate and survival of L.vannamei at 250 and 500 mg?kg-1 COS (P0.05); there is significant difference in peroxidase activity of L.vannamei at 250 mgkg-1 COS (P0.05); the acid phosphatase activity and lysozyme activity of L.vannamei at 500 mgkg-1 COS are significantly improved (P0.05); there is no significant difference in the total superoxide dismutase activity at 250 mgkg-1and 500 mgkg-1 COS (P0.05). In conclusion, 250~500 mgkg-1 COS can improve the cell immunity and total activity of humoral immune factor, increasing the growth rate and survival of L.vannamei.