PROBLEM TO BE SOLVED: To provide a carcinogenesis promotion inhibitor which effectively inhibits the carcinogenesis promotion of cells.SOLUTION: The carcinogenesis promotion inhibitor includes a polymer composition derived from a tea leaf as an active constituent. As the polymer composition derived from a tea leaf, a fraction obtainable by removing a low molecular weight component with a molecular weight of <10,000 from the water-soluble extract of a tea leaf by ultrafiltration is used.