A cellulose ester and film thereof useful for remarkably improving optical properties such as optical isotropy are provided. The cellulose ester is adjusted so that the degree of substitution is from 2.90 to 2.965, the total of degrees of substitution at 2- and 3-positions is not less than 1.97, and the half height width of chemical composition expressed in degree of substitution is not more than 0.09. Such a cellulose ester maybe produced by a method for producing a cellulose ester, which comprises (i) an acylating step for acylating a cellulose with an acylating agent in the presence of a sulfuric acid catalyst, and (ii) a hydrolyzing step for hydrolyzing the acylated product in the presence of a sulfuric acid catalyst, and in which the acylation carried out with from 1.40 to 2.0 molar equivalents of the acylating agent relative to 1 mol of a hydroxyl group in the cellulose in the presence of 6.5 to 9.5 parts by weight of the sulfuric acid catalyst relative to 100 parts by weight of the cellulose in the acylating step (i).