Reaction of the alkyl ketene dimer and hydroxyl radicals in the presence of catalysts was studied.Tetradecyl ketene dimer was chosen as the alkyl ketene dimer.p-Toluen sulfonic acid, KOH and KHCO3 were used as the catalysts. Primary, sec-, tert-BuOH, ethylene glycol, phenol and H2Owere used as the hydroxyl radicals.As a result, the reaction products of alkyl ketene dimer with hydroxyl radicals, except H2O, were esters of 2-alkyl-3-keto acid.Basic catalysts gave larger reaction velocity than acidic catalysts to hydroxyl radicals with the exception of phenol. Sec-, tert-BuOH and H2O which were difficult to react by the acidic catalysts, have readily reacted comparatively by using basic catalysts and the ketone was obtained with H2O. The ester of keto acid was obtained by using KHCO3 and by a small quantity of KOH. However, ketone was obtained with KOH by using more than equivalent of the alkyl ketene dimer.