Oxygen diffusivity was examined in the oxide scales formed on Fe-Cr alloy surface and Mn-Co spinel coating layer. The stable isotope oxygen (O-18(2)) was adopted to visualize the diffusion profiles of oxygen in the oxide scales and coating layer. A relatively fast diffusivity of O-18 was observed (diffusion coefficients were 10(-12) cm(2) s(-1) orders of magnitude at 1073 K) in the oxide scale. MnCo2O4 spinel coating was examined on the Fe-Cr alloy surface to clarify the O-18 diffusion in the coating oxide layer. Two drops of O-18 diffusion profiles were observed in the MnCo2O4 spinel coating layer; first one was at surface region and second was MnCo2O4 spinel coating/alloy interface. Relatively fast O-18 diffusion coefficients were observed on the Mn-Co spinel surface (the diffusivities of O-18 were 10(-13) 10(-12) cm(2) s(-1) at 1073 K). A significant fast diffusivity of O-18 was observed in the middle of the MnCo2O4 spinet coating. The second drop of O-18 concentration can be related to the existence of Cr around the MnCo2O4 spinel coating/alloy interfaces. The growth Fate of oxide scale was controlled by the existence of Cr around the oxide scale/alloy or oxide coating/alloy interfaces. (C) 2008 Elsevier B.V. All rights reserved.