A thin film of zinc hexacyanoferrate (ZnHCF) was formed directly on a Zn electrode to prepare a chemically modified electrode. The electroactive film was strongly attached to the electrode surface and was stable against gradual dissolution during potential cycling and long-term usage. The voltammetric characteristics of the directly modified ZnHCF film electrode were also investigated in the presence of different alkali metal cations. In view of the fact that, unlike the other transition metal hexacyanoferrates, ZnHCF film can be generated only at a certain ratio of modifier species, the modification process has an essential role in the nature and properties of the generated electroactive film. Due to the mechanism of the direct modification process, concentrations of the modifier species including Zn2+ and Fe(CN)(6)(3-) have no effect on the nature of the generated electroactive film. Thus, by using direct modification, the film formation is not affected by the ratio of Zn2+/Fe(CN)(6)(3-), as this ratio is kept at 1: 1 for any possible case. This results from the fact that, by involving a mole of Fe(CN)(6)(3-) in the surface reaction (the reaction which occurs at the electrode surface and causes the formation of the ZnHCF film), only a mole of Zn2+ dissolves from the electrode surface to share in the surface reaction (plus a mole of K+ from the supporting electrolyte). The electrocatalytic properties of the modified electrode for oxidation of thiosulfate were also investigated.