We have conducted an electrical power generation experiment using a single cell of solid oxide fuel cell (SOFC) with (Ba0.3Sr0.2La0.5)InO2.75 as an electrolyte at an operating temperature of 800 degrees C. A moistened 10% hydrogen/argon mixture constituted the fuel gas, and air was the oxidant gas. As cathode and anode materials, we selected (La0.6Sr0.4)(Mn1-xFex)O3-delta (x=0-0.6) and Ni, respectively. The power density proved to be dependent on the Fe content of the cathode; use of (La0.6Sr0.4)(Mn0.6Fe0.4)O3-delta as a cathode material enabled us to reach a maximum power density of 0.58 W/cm(2). An analysis of X-ray Absorption Near-Edge Structure (XANES) taken to detect mixed valence of Mn and Fe showed that each valence was over 3.0. We also investigated, by X-ray diffraction and energy dispersive X-ray analysis (EDX), the diffusion of the constituent elements around the interface between the cathode and the electrolyte. Our results showed that the Mn, Fe and In diffused to the opposite phase. The interface resistance between electrolyte and electrode, which was measured by the direct current two-probe method, reached a minimum value at x=0.4, suggesting that the electronic conductivity of the interface would strongly affect the power generation. (c) 2005 Elsevier B.V. All rights reserved.