Background: Methanol is abundant, safe, and environmentally friendly and has physicochemical properties similar to those of gasoline. It is a promising alternative fuel in China because it can be directly used in both spark- and compression-ignition internal combustion engines. The current development of spark-ignition engines focuses on the reduction of the fuel volume and increase in the compression ratio (CR), which would benefit the engine’s thermal efficiency. However, increasing the CR may deteriorate particulate matter (PM) due to the high temperature.Methods: Herein, an experimental study was conducted on methanol–gasoline blends in a spark-ignition engine. We examined the performance and formaldehyde emissions of methanol–gasoline blends by using three volume fractions (M0, M15, and M100). In addition, the effects of the CR on PM emissions were investigated.Results: The following relationships were observed: (1) When methanol was blended with gasoline, the formaldehyde emissions increased significantly. The formaldehyde emissions of 100% methanol were higher than those of the methanol–gasoline blend with a methanol volume fraction of 15%; both of these emissions were higher than those of pure gasoline; (2) Increasing the CR resulted in increased PM emissions; (3) For a given blending ratio, the PM emissions were positively correlated with the CR; and (4) The PM emissions were negatively correlated with the methanol volume fraction.Conclusions: Methanol reduces the heat loss at the wall surface. As the ratio of methanol in gasoline increases, the PM emissions decrease. On the other hand, the PM emissions are positively correlated with the CR. The addition of lower alcohols dilutes the concentrations of soot precursors, thereby reducing the soot emissions.