Oxidative stress has been proposed to be involved in colorectal cancer development. Many dark pigmentsof plants have potent oxidative stress preventive properties. In this study, unpolished Thai rice was assessedfor antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) methods. Red strain unpolished Thai rice was also administered to rats exposed toazoxymethane (AOM) for induction of aberrant crypt foci (ACF). Serum malondialdehyde (MDA) and ferricreducing antioxidant power (FRAP) were investigated for cellular oxidative stress and serum antioxidants,respectively. Red pigment unpolished Thai rice demonstrated high antioxidant activity and was found tosignificantly and dose dependently decrease the total density and crypt multiplicity of ACF. Consumption of Thairice further resulted in high serum antioxidant activity and low MDA cellular oxidative stress. Interestingly, thedensity of ACF was strongly related to MDA at r = 0.964, while it was inversely related with FRAP antioxidants(r = -0.915, p < 0.001). The results of this study suggest that the consumption of red strain of unpolished Thairice may exert potentially beneficial effects on colorectal cancer through decrease in the level of oxidative stress.