To provide an optical film which exhibits excellent retardation values both in the film plane and along the direction perpendicular to the film plane and shows little change in retardation values depending on environmental factors such as humidity, a liquid crystal display showing little change in viewing angle characteristics due to an environmental (humidity) change, and a polarizing plate to be used in the liquid crystal display, the cellulose acylate contains a cellulose acylate which is a mixed fatty acid ester of a cellulose and satisfies formulae specified in the specification, and a polarizing plate and a liquid crystal display using this cellulose acylate film.