There is provided a method for producing hydroxypropyl methyl cellulose acetate succinate (HPMCAS), including an esterification step of reacting hydroxypropyl methyl cellulose with an acetylating agent and a succinoylating agent in the presence of an aliphatic carboxylic acid in a kneader reactor equipped with two or more stirring blades rotating around their own axes and orbitally revolving, to obtain a reaction product solution containing HPMCAS; a precipitation step of precipitating the HPMCAS by mixing the reaction product solution with water to obtain a suspension of the precipitated HPMCAS; and a washing and recovery step of washing the HPMCAS in the suspension and recovering the washed HPMCAS. Further, there is provided HPMCAS having yellowness at 20° C. of 15.0 or less, as determined in a 2% by mass solution of the HPMCAS in a mixed solvent of dichloromethane, methanol and water in a mass ratio of 44:44:10.