Abstract: BACKGROUND ＆ AIM: To evaluate the chronic toxic effects of trivalent and hexavalent chromium to rats. MATERIALS AND METHODS: Groups were set up on the basis of 10％ LD50,6％ LD50,2％ LD50 ,and the negative control group simultaneously.After ninety_days feeding test, the serum and histopathological indexes and the ratio of viscera and body were assessed. RESULTS: The CHO,HDL,TG,Glu were significantly decreased in high_dose group of CrCl3 and control group(P<0.05).The body weight gradual decreased with increasing doses of K2Cr2O7,and the difference were significant compared with control group(P<0.05).The erythrocyte count were significantly higher than that of control group(P<0.05)，and lymphocyte were significantly lower.Serum ALT,BUN,Cr were raised but HDL,TG,Glu were decreased in the high_dose group of K2Cr2O7 and were significantly higher than that of control group.Pathological the changes in the high_dose group of K2Cr2O7 showed hepatic sinus dilation and congestion, mild exudative hemorrhage,and focal necrosis was found. CONCLUSION: K2Cr2O7 could damage the immunologic system,liver and kidney．The chronic toxicity of K2Cr2O7 was obviously higher than CrCl3.

Key words: chromium, chronic toxicity