Terminal voltage, electric power density and overpotential were measured for the solid oxide fuel cell with gadolinium-doped ceria electrolyte (Ce0.8Gd0.2O1.9, GDC), 30 vol% Ni-GDC anode and Pt cathode using a H2 fuel or biogas (CH4 47, CO2 31, H2 19 vol %) at 1073 K. Addition of 1 ppm H2S in the 3vol % H2O-containing H2 fuel gave no change in the open circuit voltage (0.79 - 0.80 V) and the maximum power density (65 - 72 mW/cm2). Furthermore, no reaction between H2S and Ni in the anode was suggested by the thermodynamic calculation. On the other hand, the terminal voltage and electric power density decreased when 1 ppm H2S gas was mixed with the biogas. After the biogas with 1 ppm H2S flowed into the anode for 8 h, the electric power density decreased from 125 to 90 mW/cm2. The reduced electric power density was also recovered by passing 3 vol % H2O-containing H2 fuel for 2 h.