A novel family of metal oxides with a chemical formula of Sr2Ce1-xPrxO4 (x = 0, 0.2, 0.5, 0.8, and 1) was developed as mixed oxide ion and electronic conductors for solid oxide fuel cells (SOFCs). All of the investigated samples were synthesized by the ceramic method at 1000 degrees C in air and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). Ex-situ PXRD reveals that the Sr2PbO4-type Sr2CeO4 decomposes readily into a mixture of perovskite-type SrCeO3 and rock-salt-type SrO at 1400 degrees C in air. Surprisingly, the decomposed products are converted back to the original Sr2PbO4-type Sr2CeO4 phase at 800 degrees C in air, as confirmed by in-situ PXRD. Thermal decomposition is highly suppressed in Sr2Ce1-xPrxO4 compounds for Pr > 0, suggesting that Pr improves the thermal stability of the compounds. Rietveld analysis of PXRD and SAED supported that both Pr and Ce ions are located on the 2a site in Pbam (space group no. 55). The electrical transport mechanism could be correlated to the reduction of Pr and/or Ce ions and subsequent loss of oxide ions at elevated temperatures, as shown by TGA and in-situ PXRD. Conductivity increases with Pr content in Sr2Ce1-xPrxO4. The highest total conductivity of 1.24 x 10(-1) S cm(-1) was observed for Sr2Ce0.2Pr0.8O4 at 663 degrees C in air.