The synthesis of nanocrystalline La2-xSmxMo2O9 (0 <= x <= 0.6) oxide-ion conductors by a microwave assisted-combustion method using aspartic acid as a combustion fuel is presented. A single-phase Sm-doped La2Mo2O9 nanopowders (similar to 25 nm) were produced within 45 min. The Sm-doping (x >= 0.2) effectively suppressed the alpha ->beta phase transition of pure La2Mo2O9 and maintained the high temperature cubic phase at room temperature. The synthesized nanocrystalline Sm-doped samples had good sinterabilty and relatively a low sintering temperature of 800 degrees C for 5 h was sufficient to reach similar to 98% of its theoretical density. Sm-doping effectively improved the oxide ion conductivity of La2Mo2O9 and the maximum oxide-ion conductivity of 0.196 S cm(-1) was attained at 750 degrees C for of La1.7Sm0.3Mo2O9. (C) 2015 Elsevier Ltd. All rights reserved.