A method for producing a cellulose acylate having a predetermined substitution degrees, which comprises acylating cellulose with an esterifying agent that contains an excessive amount of an acid anhydride relative to the hydroxyl group of cellulose, and mixing the reaction mixture with a water-containing reaction stopper to thereby hydrolyze the acid anhydride while controlling the temperature of the reaction mixture to fall between -30.degree. C. and 35.degree. C.