Nano-crystalline Sr2MgMoO6-delta (SMMO) powders were synthesized successfully by a novel sol-gel thermolysis method using a unique combination of polyvinyl alcohol (PVA) and urea. The decomposition behavior of gel precursor was studied by thermogravimetric-clifferential thermal analysis (TG/DTA) and the results showed that the double-perovskite phase of SMMO began to form at 1000 degrees C. The microstructure of the samples had been investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). XRD patterns confirmed that well-crystalline double-perovskite SMMO powders were obtained by calcining at 1450 degrees C for 12 h. TEM morphological analysis showed that SMMO powders had a mean particle size around 50-100nm. The SAED pattern and Raman spectroscopy showed that the SMMO powders were nano-polycrystalline well-developed A(B-0.5'B-0.5 '')O-3 type perovskite material. The XPS results demonstrated that the Mo ions in SMMO had been reduced after exposure to H-2. The electric property was studied by four-probe method. The results showed that conductivity was 8.64 S cm(-1) in 5.0% H-2/Ar at 800 degrees C and the activation energies at low temperatures (400-640 degrees C) and high temperatures (640-800 degrees C) are about 21.43 and 6.59 kj mol(-1), respectively. (C) 2008 Elsevier B.V. All rights reserved.