Abstract: ObjectiveIn order to study the effects of cadmium in water on immunity of fish.MethodCarassius auratus was selected as the target fish and was raised in water with different concentrations of CdCl₂.On the 10^th day,fish were killed and weighted,immune indexes,including total blood leucocyte numbers,serum lysozyme level,phagocytic rate and phagoindex of macrophage in pronephros,were determined.ResultsThe results showed that,total blood leucocy te numbers of fish in low concentration of Cd(2.5μg/L)was significantly higher than that of control fish,while no difference existed among Cd 5.0μg/L,Cd 10.0μg/L and control.With the growth of cadmium concentration, there is an increasing tendency in serum lysozyme level,and lysozyme of fish in high dose of Cd(10.0μg/L)was significant higher than that of control.Besides,there were no differences in phago cytic rate and phagoindex of macrophage in pronephors among various groups.ConclusionOur research indicated that Cd can induce immunotoxicity to Carassius auratus,research on effect of exnobiotics on fish immune function can be used as an effective biomarker in assessing water pollution.