Abstract: 【Abstract】Objective To investigate the effect of CYP3A4 activity on aflatoxin B₁(AFB₁)-induced hepatocarcinogenesis in Wistar rats. Methods 45 Wistar rats were grouped randomly into AFB₁-teatment (group A) and the control (group B). Rats in group A were injected with AFB₁ through abdomen，1-3 times per week with the dosage 200μg/kg of body weight. Liver biopsies were performed on all animals during the 13^th-，23^rd-，33^rd-，43^rd-，53^rd- and 63^rd- week of the experiment，and the animals were executed at the 73^rd- week. CYP3A4 activity was examined on each liver sample by the method of fluorescence quantitation. Results In group A，CYP3A4 activity increased gradually from the beginning of the experiment，reached the highest value at the 23^rd-week and then decrease gradually，increased again at the 43^rd-week，which formed a double peaks and the differences among the stages were significant (P=0.000). In group B，CYP3A4 activity decreased significantly at the 33^rd- and 63^rd-week but little change was observed in the other stages. The most obvious difference between group A and B was at the 63^rd-week but the difference was not statistically significant (P=0.638). Conclusion AFB₁ might inhibit the activity of CYP3A4 during the process of hepatocarcinogenesis of rats，by which to promote the resistance of early cancer cells against gene toxicity and then to develop liver cancer.

Key words: 【Key words】 Cytochrome CYP 3A4, Aflatoxin B₁, Hepatocellular carcinoma