In operating biogas-fueled SOFC module, impurities such as H2S and siloxane can poison reforming catalyst and anode. To achieve a stable SOFC operation, fuel impurity poisoning of Ru/γ-Al2O3 catalyst has to be examined. Poisoning test for the reformer and the reformer-SOFC series were performed at 700oC. Humidified simulated biogas with varied concentration of H2S or siloxane was supplied to Ru/γ-Al2O3 beads-packed reformer. H2S poisoning test during biogas steam reforming showed a correlation between the degradation rate of CH4 conversion and the decrease rate of Ru surface area which increased with increasing H2S concentration. In the case of siloxane poisoning test, accumulated-silica covered the catalyst surface, resulting in the degradation of CH4 conversion although milder than the case of H2S. The poisoning tests for the reformer-SOFC series revealed that the degradation rate of cell voltage was considerably lower than that of CH4 conversion in the reformer for both impurities.