The present invention is to provide an optical film which exhibits low hygroscopicity, high transparency, high heat resistance and markedly lowered brittleness, and particularly to provide an optical film which is appropriately employed as a polarizing plate protective film for large liquid crystal display devices and outdoor liquid crystal display devices. The above optical film is characterized in that acrylic resin (A) and cellulose ester resin (B) are incorporated at a weight ratio of 95:5-30:70, weight average molecular weight Mw of aforesaid acrylic resin (A) is at least 80,000, total substitution degree (T) of the acyl group of aforesaid cellulose ester resin (B) is 2.0-3.0, the substitution degree of the acyl group having 3-7 carbon atoms is 1.2-3.0, and weight average molecular weight Mw of aforesaid cellulose ester resin (B) is at least 75,000. It is characterized that the total substitution degree of the acyl group other than carbon atoms of 3-7 of the cellulose ester resin (B) is at most 1.3.