This study focused on measurement of the autothermal reforming of biogas over a Ni based monolithic catalyst. The effects of the steam/CH4 (S/C) ratio, O2/CH4 (O2/C) ratio and temperature were investigated. The CH4 conversions were higher under all examined temperatures than the equilibrium conversion calculated using the blank outlet temperature, because the catalyst layer was heated by the exothermic catalytic partial oxidation reaction. The CH4 conversion increased with increasing O2/C ratio. Moreover, the CH4 conversion was higher than the equilibrium conversion calculated using the blank outlet temperature for O2/C>0.42 and reached about 100% at O2/C=0.55. However, the hydrogen concentration decreased for O2/C>0.45 because hydrogen was combusted to steam in the presence of excess oxygen. On the other hand, the hydrogen and CO2 concentrations increased and the CO concentration decreased with increasing S/C ratio. As a result, it was found that the highest hydrogen concentrations and CH4 conversions were attained at the O2/C ratios of 0.45～0.55 and the S/C ratios of 1.5～2.5.Moreover,the H2/CO ratio could also be controlled in the range from about 2 to 3.5 to give at least 90%CH4 conversion,by regulating the O2/C or S/C ratios. The results focused on measurement of the autothermal reforming of biogas over a Ni based monolithic catalyst. The effects of the steam / CH4 (S / C) ratio, O2 / CH4 (O2 / C) ratio and temperature were investigated. higher under all monitored temperatures than the equilibrium conversion calculated using the blank outlet temperature, because the catalyst layer was heated by the exothermic catalytic partial oxidation reaction. The CH4 conversion increased with increasing O2 / C ratio. equilibrium conversion calculated using the blank outlet temperature for O2 / C> 0.42 and reached about 100% at O2 / C = 0.55. However, the hydrogen concentration decreased for O2 / C> 0.45 because hydrogen was combusted to steam in the presence of excess oxygen On the other hand, the hydrogen and CO2 concentrations increased and the CO concentration decreased with increasing S / C ratio. As a result, it was found that the highest hydrogen concentrations an d CH4 conversions were attained at the O2 / C ratios of 0.45-0.55 and the S / C ratios of 1.5-2.5. Moreover, the H2 / CO ratio could also be controlled in the range from about 2 to 3.5 to give at least 90 % CH4 conversion, by regulating the O2 / C or S / C ratios.