PURPOSE: To produce cellulose acetate in a short time and to make it possible to utilize a somewhat low grade material, by acetylating activation-treated cellulose with an acid mixture containing a small amount of an acid catalyst at high temperatures and hydrolyzing the product at high temperatures to effect aging.

CONSTITUTION: A cellulose material is subjected to activation treatment by adding thereto about 1/4 time the weight of the material, of acetic acid or a mixture of acetic and sulfuric acid and stirring the mixture for about 20W60min. The activation-treated cellulose is then acetylated by adding thereto an acid mixture containing 2W4 times of acetic anhydride and up to 1/20 time of an acid catalyst, heating the reaction mixture to a final temperature of 50W85°C over 20W60min and maintaining the reaction mixture at this temperature for 3W20min.