Bismuth-doped pyrochlore-type antimonic acids H1-3xBiSbO3.nH(2)O (0 less than or equal to x less than or equal to 0.28, n = 0.5) were prepared by solution processing using the reaction of an aqueous H2O2 solution with antimony and bismuth alkoxides, and their structural properties and proton conductivity were investigated. It was found that the Bi atoms are located in an interstitial 16d (1/2, 1/2, 1/2) site in the structure and that the proton conductivity of the doped material (x = 0.081) is enhanced by about two orders of magnitude compared to that of the pure material. The relationship between the proton conductivity and structural properties is discussed. (C) 2004 Elsevier B.V. All rights reserved.