Abstract: Objective To study the anti-tumor effect of Biejiajianwan pills and explore its mechanism.Methods Mice bearing neoplasm induced by H22 cell inoculation were randomized into 4 groups,namely the negative control group,positive control group(with cyclophosphamide treatment),and high-and low-dose Biejiajianwan pill group.The tumor-bearing mice received corresponding treatments for 15 consecutive days,after which their thymuses and spleens were isolated and weighed to calculate the thymus and spleen indices.The tumor mass was also weighed and the tumor inhibition rate calculated.Immunohistochemistry was performed to evaluate the expression intensity of proliferating cell nuclear antigen(PCNA)in the tumor tissue.Results The pills significantly inhibited the growth of the implanted tumor and reduced the expression of PCNA in the tumor.Conclusion One of the possible mechanisms of the anti-tumor effects of Biejiajian pills might be associated with the inhibition of PCNA expression in the tumor.