The transfer behavior of Keggin-type heteropolytungstate anions (1,2,3-[HSiV3W9O40](6-), [PVW11O40](4-), 1,2,3- and 1,4,9-[PV3W9O40](6-), [BVW11O40](6-), and [B12O40](5-)), across the nitrobenzene \ water interface was studied by cyclic voltammetry. A pair of voltammetric peaks due to reversible ion transfer was observed for all the polyanions. Based on measurements of the apparent ion-transfer potentials at various pH values, ionic distribution diagrams were prepared. It was found that the apparent ion-transfer potentials determined at pH 2.5 showed a good correlation with their antiviral activities. It has been suggested that the polyanion with a higher surface field strength has a stronger affinity for the binding sites of viral enzymes such as reverse transcriptase and for the surface of the target cell, and thus shows a higher inhibition activity.