The electroactive composite containing tris(2,2'-bipyridine) ruthenium(II) and 18-molybdosulfate (RuS2Mo18) was used as a bifunctional electrocatalyst to fabricate a chemically bulk-modified graphite organosilicate composite electrode (GOSE) by a sol-gel process for the first time. RuS2Mo18 covered the graphite particles homogeneously with the aid of solvent; the silicate provided a rigid porous backbone, and the methyl groups endowed hydrophobicity and thus limited the wetting section of the modified electrode. The electrochemical behavior of the RuS2Mo18-GOSE in aqueous solution was studied by cyclic voltammetry. The RuS2Mo18-GOSE presents good electrocatalytic activity not only toward the reduction of bromate, which is attributed to the function of the 18-molybdosulfate, but also toward the oxidation of arsenite, which is attributed to the function of the tris(2,2'bipyridine) ruthenium(II). Another remarkable advantage of the RuS2Mo18-GOSE is its good stability and reproducibility of surface renewal by simple polishing in the event of surface fouling. (C) 2003 Elsevier B.V. All rights reserved.