There were five tested groups of allogyogenetic silver crucian carp which were fed on basal diets supplemented with 0%,0.3%,0.5%,1.0%,2.0% chitosan respectively. Each group was triplicated. After two months feeding , lysozyme activities of spleen, head kidney, serum and phagocytic activity of the leucocyte were measured. The results showed that 0.5% or 1.0 % chitosan efficiently advanced lysozyme activities ( P < 0.01) and phaogocytic activities(P <0.01) . 0.5% chitosan supplemented to the diet was optimum.