Abstract: Objective To investig ate the inhibition effect of ursodeox ycholic acid(UDCA)on colon cancer and its potential mechanism in 1,2-dimethylhy drazine-treated ICR mice.Methods After acclimation for 1 week,ICR mice were randomly divided into three groups according to weight.One group was blank control and the mice of other two g roups were injectedi.p.with DMH(30 mg/kg穊w)in 1mmo l/LEDTA once a week fo r 6 weeks.One group was UDCA group fed with AIN-93 diet with UDCA(3g/kg)from the 7th week.The other group(DMH group)and control group mice were fed with AIN-93 diet.A fter 28 weeks,all mice were killed.The mucous membrane of colon was obtained and the activity and expression of alk-SM ase were analyzed.Results Compared with DMH group,the number and malig nant degree of colon tumors in UDCA group was significantly decr eased(t=2.77,P<0.05).F urthermore,the alk-SM ase activity of UDCA group in colon mucosa and content was 22.56% and 28.97% respectively.The activity of colon content increased about 14 times and the expressio n of alk-SM ase was significantly increased in UDCA group compared with DMH g roup.Conclusion Long-term administration of UDCA could inhibit the carcinogenesis of colon cancer in DMH-treated ICR mice and the potential mechanism of UDCA chemoprev ention of colon cancer is regulating up the activity and expression of alk-SM ase.