Indole-3-carbinol (I3C), one of naturally occurring main components in cauliflower vegetables, is supposed to have a chemopreventive potential in experimental animals and humans. This study was investigated to examine chemopreventive effect of I3C on colon carcinogenesis induced by azoxymethane (AOM) using C57BL/6J mice. Mice were divided into three groups (10 or 9 mice/group). All mice were subcutaneously injected with AOM (5 mg/kg body weight, four times at weekly interval). After AOM treatment, animals of group 1 were fed by AIN-76A pellets as a basal diet. Animals of groups 2 and 3 were given I3C containing diets (100 and 300 ppm in diets, respectively) for 6 weeks until sacrifice. All mice were sacrificed at week 10 and the aberrant crypt foci (ACF) of the colonic mucosa were assessed after staining with methylene blue. Total numbers of ACF/colon in group 2 ($10.1{pm}5.1$) or group 3 ($10.6{pm}5.3$) were decreased compared to the values of group 1 ($14.4{pm}10.2$). Among numbers of ACF formation, 5, 7, 8 and 10 ACF in group 2 and 3 were greatly different those of group 1. Total numbers of aberrant crypts (AC)/colon of group 2 ($20.1{pm}10.1$) or group 3 ($22.0{pm}10.9$) were decreased compared to the value of group 1 ($33.7{pm}24.7$). Taken together, it suggests that I3C treatment may retard mouse colon carcinogenesis even after administration of AOM.