A safer dyestuff for hair colouring, catechinone, was prepared from (+)-catechin introducing O₂ into basic water / ethanol mixed solution substituting for aqueous solution in order to increase the production efficiency. The solubility of (+)-catechin in water / ethanol solution is much higher than that in water, and 34 times higher concentration of (+)-catechin was adopted for the preparation in the mixed solution. The results show that the amount and rate of catechinone production in the mixed solution are much increased as compared with those in aqueous solution. The amount of catechinone produced for the water / ethanol system is 27 times larger than that for the aqueous system. The amount and rate of the production increase with the basicity of the solution, as increasing with added triethanol amine, diethanol amine or monoethanol amine in this order.