Zirconium phosphate sulfophenylenphosphonates of general formula Zr(HPO4)(2-x)(SPP)(x)(.)nH(2)O, with SPP=O3PC6H4SO3H and x in the range 0.4-1.35, were precipitated from solutions containing H3PO4, H2SPP and ZrF62-. The SPP/HPO4 ratio in the solids is equal to the H2SPP/H3PO4 ratio in the starting solutions for x <= I and lower for x > 1. The results coming from P-31 MAS NMR. X-ray powder diffraction, FTIR-PAS spectroscopy and density measurements, as well as from the intercalation of alpha,omega-alkyl diamines in Zr(HPO4)(1.00)(SPP)(1.00), suggest that the solids have a layered structure built up by the packing of symmetric a-layers where SPP and HPO4 groups are uniformly distributed on both layer faces. Proton conductivity, at 100 degrees C and 70% relative humidity, increases with x and reaches a maximum of 0.04 S cm(-1) for x = 1.35. The conductivity of Zr(HPO4)(0.65)(SPP)(1.35)(.)nH(2)O was determined as a function of the water content at 100 degrees C and compared with that of Nafion 117 and of a sulfonated polyetherketone. (c) 2005 Elsevier B.V. All rights reserved.