Zirconium tricarboxybutylphosphonate, Zr(O3PC(CH2)(3) (COOH)(3))(2), was synthesized to prepare inorganic/organic composite membranes based on polybenzimidazole (PBI). The characteristics of zirconium tricarboxybutyl-phosphonate (Zr(PBTC)) and of the membranes formed by this and PBI were studied by X-ray diffraction, FTIR, and TG analysis. Both the compacted powers Zr(PBTC) and the Zr(PBTC)/PBI membranes were thermally stable and the conductivities measured on Zr(PBTC) and a sample of the PBI-based membrane with 50 wt.% Zr(PBTC) gave values of 6.74 x 10(-2) and 3.82 x 10(-3) S cm(-1) at 200 degreesC under PH2O/P-s = 1, respectively. The treatment to make PBI with charactetistic of proton conductivity influenced positively the proton conductivity of PBI-based membrane with 50 wt.% Zr(PBTC). This membrane presented a proton conductivity of 5.24 x 10(-3) S cm(-1) under the same measurement conditions. (C) 2004 Elsevier B.V. All rights reserved.