Diallyl sulfide (DAS), a flavoring compound derived from garlic, is considered to have cancer chemopreventive potential in experimental animals and humans. This study was designated to examine possible chemopreventive effects of DAS on colon carcinogenesis using genetically engineered transgenic Apc Min/+ mice, a well-established animal model for familial adenomatous polyposis (FAP) and sporadic colorectal cancer. Male C57BL/6J-Apc Min/+ mice were divided into three groups. Animals of group 1 were placed on the basal diet (AIN-76A) as non-treated controls. Animals of groups 2 and 3 were given DAScontaining diets (in doses of 100 and 300 ppm, respectively). All mice were sacrificed at the end of week 10 of the experiment. Histopathological investigation revealed that the incidence of colonic polyps was decreased dose-dependently by 19% (13/16) in group 2 and by 32% (13/20) in group 3 compared to the 100% incidence (10/10) in group 1. The multiplicity of colonic polyps per mouse was also slightly decreased by DAS treatment (1.88±0.35 in group 2 and 1.63±0.36 in group 3) compared to 2.00±0.39 in group 1. On the other hand, there were no significant differences in the numbers of total polyps per mouse in the small intestine between the groups. Taken together, we suggest that DAS may exert promising inhibitory effects on colon carcinogenesis in the transgenic Apc Min/+ mice.