Moringa oleifera Lam (horseradish tree; tender pod or fruits) is a major ingredient in Thai cuisine and has 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 investigate chemopreventive effects on azoxymethane (AOM)-initiated and dextran sodium sulfate (DSS)-promoted colon carcinogenesis in mice. Male ICR mice were divided into 8 groups: Group 1 served as a negative control; Group 2 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 at the designed doses above for 2 weeks prior to AOM, during and 1 week after DSS administration. At the end of the study, colon samples were processed for histopathological examination. PCNA indices, and iNOS and COX-2 expression were assessed by immunohistochemistry. The results demonstrated the incidences and multiplicities of tumors in Groups 6-8 to be decreased when compared to Group 2 in a dose dependent manner, but this was significant only in Group 8. The PCNA index was also significantly decreased in Group 8 whereas iNOS and COX-2 protein expression were significantly decreased in Groups 7 and 8. The findings suggest that M. oleifera Lam pod exerts suppressive effects in a colitis-related colon carcinogenesis model induced by AOM/DSS and could serve as a chemopreventive agent.