Cellulose ester and film thereof useful for remarkably improving optical properties, e.g., optical isotropy. The cellulose ester has a degree of substitution from 2.90 to 2.965, a total of degrees of substitution at 2- and 3-positions ≧1.97, and a half height width of chemical composition expressed in degree of substitution of ≧0.09. The cellulose ester maybe produced by (i) acylating a cellulose with an acylating agent in the presence of a sulfuric acid catalyst, and (ii) hydrolyzing the acylated product in the presence of a sulfuric acid catalyst, wherein the acylation carried out with 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).