Double-perovskite Sr2-xSmxMgMoO6-delta (SSMM, 0 <= x <= 0.8) is investigated as a possible anode material for solid-oxide fuel cells on La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) electrolytes. Single-phase SSMM samples with 0 <= x <= 0.4 are prepared. At x >= 0.6, a small amount of SrMoO4 and Sm2O3 impurities are observed. The Mg/Mo ordering in SSMM decreases with increasing Sm content. Substitution of Sm for Sr significantly improves the electrical conductivity of SSMM. At x = 0.6, the sample yields the highest conductivity, with values reaching 16S cm(-1) in H-2 at 800 degrees C. The maximum power densities of single cells achieved with x = 0.0, 0.2, 0.4, 0.6, and 0.8 anodes on a 300 mu m-thick LSGM electrolyte are 693, 770, 860, 907, and 672 mW cm(-2), respectively, in H-2 at 850 degrees C. The SSMM sample with x = 0.4 is considered as the best anode candidate because of the impurity formation seen in x >= 0.6 samples. The x = 0.4 sample not only has a thermal-expansion coefficient closer to that of the LSGM electrolyte but also exhibits good electrochemical performance and stability in commercial city gas containing H2S, where the maximum power density achieved is 726 mW cm(-2) at 850 degrees C. (C) 2011 Elsevier B.V. All rights reserved.