Single phase SrFe1.2Co0.3Ox sample with layered crystal structure was prepared using a solid state reaction method. Electrical conductivity and apparent oxygen diffusion coefficients of the SrFe1.2Co0.3Ox sample were measured as functions of temperature in atmospheres of various oxygen partial pressures \documentclass[12pt]{minimal}
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$$({\text{P}}_{{\text{O}}_{\text{2}} } )$$
\end{document}. Total and ionic conductivities were determined by using the conventional four-probe and electron blocking four-probe methods, respectively. The apparent oxygen diffusion coefficient was derived from the time-dependent conductivity relaxation data of the reequilibrium process after abruptly changing the \documentclass[12pt]{minimal}
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$$({\text{P}}_{{\text{O}}_{\text{2}} } )$$
\end{document} in the surrounding atmosphere. Several atmospheres of different \documentclass[12pt]{minimal}
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$$({\text{P}}_{{\text{O}}_{\text{2}} } )$$
\end{document} were established by the use of premixed gas cylinders. The conductivity of SrFe1.2Co0.3Ox increases with increasing temperature and \documentclass[12pt]{minimal}
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$$({\text{P}}_{{\text{O}}_{\text{2}} } )$$
\end{document}. At 900°C in air, the total conductivity and ionic conductivity are 10 and 8 S · cm-2, respectively. The ionic transference number (≈ 0.8 in air) does not have strong temperature dependence. The activation energy increases with decreasing \documentclass[12pt]{minimal}
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$$({\text{P}}_{{\text{O}}_{\text{2}} } )$$
\end{document}. In air, the activation energy has a low value of ≈ 0.37 eV. The apparent oxygen diffusion coefficient was \documentclass[12pt]{minimal}
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$$ \approx 2 \times 10^{ - 6} {\text{ cm}}^{\text{2}} \cdot {\text{s}}^{{\text{ - 1}}}$$
\end{document} at 950°C over a wide range of \documentclass[12pt]{minimal}
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$${\text{P}}_{{\text{O}}_{\text{2}}} (1 \leqslant {\text{P}}_{{\text{O}}_{\text{2}}} \leqslant 10^{ - 18} {\text{atm}})$$
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