Male Donryu rats were fed with 3-methyl aminoazobenzene(DAB). Phosphatidic acid m tabolism in the liver at 20, 40, 60, 80 and 100 th day of DAB-feeding rats was studied and compared with the normal ones. The phosphatidic acid metabolism, especially, the pass way of diglyceride synthesis in DAB-feeding rat liver with the phosphatidic acid phosphatase studied in vitro. The fed with 3-methyl-DAB was induced hepatoma on the 40 th day and the grades of hepatomas were gradually accelerated. At 80 th day, livers were almost occupied with hepatomas. The enzymatic activity of phosphatidic acid phosphatase was most elevated at 80 th day of DAB-feeding rat liver.