Colorectal cancer was induced by subcutaneous injection of 1,2-dimethylhydrazine (DMH) in mice, and the animals were administered orally with 0.4% of tea polyphenols (TP) simultaneously for 20 weeks to study its preventive effects. Results showed incidence of colorectal cancer in mice administered with TP was significantly lower than in positive controls (P < 0.05), and average number of tumor foci and proportion of adenocarcinoma were significantly fewer in TP group than in positive controls (P < 0.01). Level of cytochrome P450 (CP450) in liver microsome of the mice administered with TP was lower than that both in negative and positive controls (P < 0.01), and activities of superoxide dismutase (SOD) in liver tissue were higher than those in positive controls (P < 0.01), but lower than in negative controls (P < 0.01). Proliferative index of epithelial cells in mice was not obviously influenced by TP. It suggested that TP could have preventive effects on experimental colorectal cancer with a possible mechanism of lowering CP450 and increasing the activity of SOD in the liver.