New 5'-nucleotidase inhibitors designated as NPF-88BU-IA, NPF-88BU-IB, NPF-88BU-IIA and NPF-88BU-IIB, respectively, were i solated from the seeds and skin of th wine grape "Koshu". They were purified by solvent extraction, dialysis, and reversed-phase high performance liquid chromatography (HPLC).Their physico-chemical properties revealed these compounds to be polyphenolic substances.The average relative molecular masses of the four were estimated by gel permeation chromatography (GPC) analysis to be 7850, 5950, 11900, and 11300, respectively. They Strongly inhibited 5'-nucletidase activities from snake venom and rat liver membrane, and displayed significant therapeutic activity against Ehrlich ascites carcinoma. They also showed inhibitory effects on the growth of Streptococcus mutans MT8148(c), a primary cariogenic bacterium. Furthermore, these 5'-nucleotidase inhibitors inhibited the glucan formation from sucrose. These results suggest that the 5'-nucleotidase inhibitors can prevent the cause of caries of tooth.