Cellulose diacetate having improved resistance to delustering in hot water is produced by acetylation cellulose in the presence of a catalyst and then hydrolyzing (or ripening) the product to form secondary cellulose acetate; wherein the catalyst in the acetylated mixture is completely neutralized before about the middle of the hydrolysis reaction at the latest and thereafter hydrolysis is carried out at a temperature of about 110.degree. to 120.degree. C. while maintaining the concentration of acetic acid in the reaction mixture at about 67 to 78% by weight based on the total weight of the acetic acid and water, the relation between the hydrolysis temperature and the concentration of acetic acid being defined by the area between and including points A, B, C and D in FIG. 2.