Moringa oleifera Lam (horseradish tree; tender pod or fruits) is a major ingredient in Thai cuisine andhas some medicinal properties. Previous studies have shown potentially antioxidant, antitumor promoter,anticlastogen and anticarcinogen activities both in vitro and in vivo. The present study was conducted to investigatechemopreventive effects on azoxymethane (AOM)-initiated and dextran sodium sulfate (DSS)-promoted coloncarcinogenesis in mice. Male ICR mice were divided into 8 groups: Group 1 served as a negative control; Group2 received AOM/DSS as a positive control; Groups 3-5 were fed boiled freeze-dried M. oleifera (bMO) at 1.5%,3.0% and 6.0%, respectively supplemented in basal diets for 5 weeks; Groups 6-8 were fed with bMO diets atthe designed doses above for 2 weeks prior to AOM, during and 1 week after DSS administration. At the endof the study, colon samples were processed for histopathological examination. PCNA indices, iNOS and COX-2expression were assessed by immunohistochemistry. The results demonstrated the incidences and multiplicitiesof tumors in Groups 6-8 to be decreased when compared to Group 2 in a dose dependent manner, but this wassignificant only in Group 8. The PCNA index was also significantly decreased in Group 8 whereas iNOS andCOX-2 protein expression were significantly decreased in Groups 7 and 8. The findings suggest that M. oleiferaLam pod exerts suppressive effects in a colitis-related colon carcinogenesis model induced by AOM/DSS andcould serve as a chemopreventive agent.