Walnuts and peanuts contain phytochemicals that exhibit properties that may prevent colon cancer development. The objective was to determine the potential of walnuts and peanuts on Azoxymethane (AOM) induced Aberrant Crypt Foci (ACF) and the activity of detoxification enzymes: Glutathione S-Transferase (GST), Catalase (CAT), and Superoxide Dismutase (SOD) in Fisher 344 male rats. After 1 week acclimatization period, 20 rats were randomly divided into 5 groups. One was fed AIN93G Control (C) diet, 4 groups were fed walnuts (W) and peanuts (P) at 5% and 10%. At 7 - 8 weeks, rats received AOM injections at 16 mg/kg body weight (subcutaneously). Rats were killed by CO₂ asphyxiation at 17 weeks. Enzyme activities GST, CAT and SOD were determined. ACF incidence in rats fed W (5% and 10%) was 131 and 95, and in those fed P (5% and 10%) was 110 and 56. Rats fed W and P had a significant (p < 0.05) percent reduction (17.92% - 65.09%) in total ACF compared to C (159). Liver GST activity (μmol/mg) in rats fed W (5% and 10%) was 3.64 and 3.98, and in those fed P (5% and 10%) was 3.84 and 3.30, compared to rats fed C (0.26). CAT activity (μmol/mg) in rats fed W (5% and 10%) was 0.57 and 0.65 and in those fed P (5% and 10%), was 0.76 and 1.26, compared to rats fed C (0.14). SOD activity (U/mg) in rats fed W (5% and 10%) was 529.38 and 576.57 and in those fed P (5% and 10%), was 293.50 and 466.95, compared to rats fed C (82.42). Feeding walnuts and peanuts, especially at 10%, significantly (p < 0.05) reduced the incidence of AOM induced ACF, likely due to the phytochemicals present in nuts.