Phytic acid (PA) (Inositol hexaphosphate, IP6) is a naturally occurring polyphosphorylated carbohydrate that is present in substantial amounts in almost all plants and mammalian cells. Recently PA has received much attention for its role in anticancer activity. In the present study, the preventive effects of PA on colon carcinogenesis were investigated. Six-week old Fisher 344 male rats were fed a AIN-93G purified diet and PA (0.5% or 2% PA in water) for 8 weeks. The animals received two (1st and 2nd week) injections of azoxymethane (AOM, 15 mg/kg b.w.) to induce colonic aberrant crypt foci (ACF). After sacrifice, the total numbers of aberrant crypts (AC) and ACF in colonic mucosa were examined after staining with methylene blue. Blood and serum were analyzed with a blood cell differential counter and an automatic serum analyzer. AOM induced the total numbers of 142.3 ± 22.3 ACF/colon and 336.6 ± 55.1 AC/colon. PA at the doses of 0.5 and 2% decreased the numbers of ACF and AC/colon in a dosedependent manner. The numbers of ACF/colon and AC/colon by PA at the dose of 0.5% were 124.4 ± 28.5 and 302.7 ± 67.3, respectively. PA at the dose of 2% significantly decreased the ACF and AC numbers to 109 ± 18.1 and 254.8 ± 50.6, respectively (p < 0.01). Especially, 2% PA significantly reduced the number of large ACF ( ≥ 4 AC/ ACF) from 26.8 ± 6.2 ACF/colon to 15 ± 6.7 ACF/colon (p < 0.01). Although some parameters in blood counts and serum chemistry were changed compared with the control, no specific toxicity was found. These findings suggest that phytic acid can be a chemopreventive agent for colon carcinogenesis resulting from inhibition of the development of ACF in the F344 rat.