Abstract: Objective Through observing the pathological change and the change of the Ras protein and p53 protein and cytokeratin 20(CK20) mRNA in bladder bladder tumor tissue induced by aristolochic acid，to evaluate the preventing effect of curcumin and explore the possible mechanism. Methods Fifty rats were divided into three groups randomly,control group,experiment group and preventive group.The rats in experimental group were given 10mg/(kg·d) of aristolochic acid for 3 months; do the same to the preventive group,and at the same time,added 2% curcumin powder to intervene; the rats in the control group received normal diet and water.After three months all of the rats were sacrificed and the bladder tissue obtained,the Ras protein,p53 protein and CK20 mRNA detected. Results After three months,the incidence of the bladder tumor of the experiment group was 95% (19/20),while that of the preventive group was 10%（2/20）.The Ras protein and p53 protein and the CK20 mRNA in control group were negative,on the contrary,they were positive in the preventive group and the experiment group.The change of experiment group was obvious,showing statistical significance （P<0.001）. Conclusion Curcumin had a preventive effect on the bladder tumor induced by aristolochic acid.The possible molecule mechanism was that curcumin can inhibit the over expression of Ras gene and p53 gene.