Abstract: The incorporations of³H leucine into protein and ³H uridine into RNA in mouse liver Were increased when PASPA was given to mice at a dose of 30 mg/kg for 4 successive days. The RNA polymerase activity, especially the RNA polymerase Ⅱ activity in the solubilized liver nuclear fraction of PASPA-treated mice was also increased. In vitro experiment demonstrated that PASPA increased the RNA polymerase activity significantly in mouse liver nuclei at a concentration of 1μg/ml. These results suggest that the enhancement of RNA polymerase activtites, particularly RNA polymerase Ⅱ activity, induced by PASPA treatment is responsible for the increase in syntheses of protein and RNA in mouse liver tissue.