The poor cold startability is one of the problems in using methanol as the fuel for Otto-type engines.A method for solving this problem is to mix some additives for cold start improvement.The effects of various additives and their concentrations on the improvement of cold startability were studied, and the following results were obtained: (1) The cold startability was studied using actual engines in relation to the preliminary results of cold mixture formation obtained by using an equilibrium air evaporation apparatus. It was found from this study that the cold startability of actual engines shows a high correlation with the excess air ratio of fuel mixture observed using the equilibrium air evaporation apparatus. It has become clear from this finding that the cold startability of Otto-type methanol engines depends greatly on the excess air ratio of the fuel mixture. (2) Using gasoline as an example of the additive for cold start improvement, the fuel vapor composition of methanol-gasoline mixtures, fuel evaporation rate which considers reduction of temperature due to the heat of fuel evaporation, air fuel ratio, stoichiometric air fuel ratio and excess air ratio of fuel vapor were calculated. It was found from this study that most of the fuel vapor is gasoline even when a small amount of gasoline is added to methanol resulting in an extremely small excess air ratio. It is obvious that this small excess air ratio is the dominant factor for improvement in cold startability.