Oxide scale formations on Fe-Cr alloy interconnects were investigated in anode gas (mixtures of CH4 and H2O) atmospheres for solid oxide fuel cells. The silicon concentration in Fe-Cr alloy changed the microstructures of oxide scales, elemental distribution and oxide scale growth rates. Oxide scale is composed of the following phases from surface to inner oxides: Fe-Mn spinel, Cr2O3, oxide scale/alloy interface and internal oxides of Si and A]. With decreasing the Si concentration from 0.4 to 0.01 mass%, formation of thin Si and Mn layer was observed inside the Fe-Cr alloy. Oxide scale growth rate constants decreased by lowering the Si concentration in Fe-Cr alloy from 4.2 x 10(-18) to 2.1 X 10(-18) m(2) S-1 at 1073 K. Diffusivity of Fe and Cr was changed by the concentration of Si in Fe-Cr alloy, which affects the growth rates of oxide scale. The electrical conductivity of oxidized Fe-Cr alloy shows almost same level regardless the Si concentration (in the orders of 10 S cm(-2) at 1073 K). (c) 2006 Elsevier B.V. All rights reserved.