To date great efforts have been devoted to the development of solid oxide fuel cell (SOFC) devices that is able to run at intermediate temperature (IT) and to retain good electrochemical, performance as in the high temperature regime. To this end, Tantalum (Ta) is doped into Sr2Fe1.5Mo0.5-xTaxO6-delta (0.0 <= x <= 0.15) to further improve the electrochemical performance as the cathode materials for IT-SOFC. Pure ortho-rhombic Sr2Fe1.5Mo0.5-xTaxO6-delta (0.0 <= x <= 0.15) samples, with space group Prima (no. 62), are synthesized by a two-step method and identified via the powder X-ray Rietveld refinements. X-ray photoelectron spectroscopy and thermogravimetry results consistently show that the number of oxygen vacancy increases with the increasing of Ta content. The thermal expansion compatibility of the samples is found to match the electrolyte of La0.9Sr0.4Ga0.1Mg0.2O3-delta (LSGM) better than that of cobalt-containing electrode compounds. Finally, the higher oxygen vacancy concentration leads to the enhanced ionic conductivity although electrical conductivity is slightly decreased due to the oxygen vacancy blocking. Therefore, Ta-doped Sr2Fe1.5Mo0.5O6-delta is proved to be a promising candidate for future cathode materials of IT-SOFC. (C) 2013 Elsevier B.V. All rights reserved.