Trachyspermum ammi seed consumed worldwide as a spice ingredient is much valued for its medicinal properties. However, it has not been investigated for its cancer chemopreventive efficacy. Herein, the chemopreventive effect of different doses (2%, 4%, and 6%) of test diets of Trachyspermum ammi seeds were examined on DMBA-induced skin and B(a)P-induced forestomach papillomagenesis, inducibility of drug metabolizing phase I and phase II enzymes, antioxidant enzymes(catalase, superoxide dismutase, glutathione peroxidase, glyoxalase I), reduced glutathione content, and peroxidative damage. Results exhibited a significant reduction in the skin as well as the forestomach tumor multiplicity with respect to all doses of test diet as compared to the control group. Biochemical assays revealed a significant increase in the activities of phase I enzymes especially with 6% test diet. A concomitant increase in the activities of the phase II enzymes and antioxidant enzymes were observed in Trachyspermum ammi treated groups. The content of reduced glutathione was significantly elevated, whereas the peroxidative damage along with lactate dehydrogenase activity exhibited a significant reduction with all the three doses of test diet. These findings were indicative of chemopreventive potential of Trachyspermum ammi seeds against carcinogenesis.