In LaNbO4, Sm, Gd and Yb were investigated as substitutes to enhance its ion conductivity, for its application in solid oxide fuel cell. La0.9M0.1NbO4 (M = Sm, Gd, Yb) was prepared via a solid state reaction route and single phase was attained by calcining the constituent oxides at 1200 degrees C for 5 h. The total conductivity of LaNbO4 was increased by partly replaced La with Sm, Gd and Yb, due to the muti-valences of the substitutions. The highest conductivity (1.76 x 10(-4) S cm(-1)) was achieved for La0.9Sm0.1NbO4 at 800 degrees C in wet air, more than one order higher compared to that of LaNbO4. The introduction of Sm, Gd or Yb also slightly increased the ion transport number of LaNbO4, indicating that the increase of the total conductivity was mainly contributed by the enhanced ion conductivity, which was beneficial for its application as a pure ion conductor. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.