To study the influence of contaminated environment on the morphology and quantity of peripheral blood cells in Carassius auratus,the fishes were sampled from two different areas:Reservoir Liujiaxia (RL),a relatively unpolluted area,as a control site; Baiyin Section of the Yellow River (BSYR),a heavier polluted area compared to RL.Blood smears were prepared by normal method and stained with Giemsa.The erythrocyte micronuclei and nuclear abnormalities and the blood cells were counted and the cells were photographed by the microscope with Motic B5 Professional Series.The results showed that the number of erythrocytes was significantly lower (P<0.05) while the numbers of erythrocyte micronuclei (P<0.01) and nuclear abnormalities (P<0.05) were significantly higher in BSYR than that in RL; Total numbers of leucocytes (P<0.05) and lymphocytes (P<0.05) increased significantly,while the total numbers of thrombocytes (P<0.05) and neutrophils (P<0.01) decreased obviously in BSYR compared to those in RL; Monocytes had a tendency to decrease in BSYR but the difference did not reach a significant level (P>0.05) between the two sampling sites.The results suggest that the environmental contamination in BSYR has been causing obvious alterations in the numbers of peripheral blood cells,the frequencies of erythrocyte micronuclei,and nuclear abnormalities in C.auratus.