An experimental study on the reforming characteristics of five different catalysts for methanol fuel was conducted and the endurance of each catalyst was examined using a fixed type reformer. A reformer utilizing the heat of exhaust gas was also designed and constructed, and the effect of blending the reformed methanol fuel to gasoline was studied in the combustion process of a spark ignition engine. Analyses of the indicator diagram show that the increase of the ratio of reformed gas and gasoline results in (1) an increase of speed and stability of combustion characteristics, (2)the extension of the lean limit of the air-fuel ratio, (3) an increase in the thermal efficiency, (4) a decrease in the cycle-by-cycle fluctuation of the combustion process, and (5) quick achievement of stability for abrupt changes in the throttle position. In view of three results, the optimum operating conditions are proposed.