An optical film that irrespective of the type of cellulose ester, realizes lowering of the melt viscosity thereof, and that realizes low melting temperature and suppressing of thermal deterioration of shaping material, and that excels in mechanical properties, optical characteristics, dimensional stability and melt formability. It is also intended to provide, making use of the optical film, a polarizing plate and liquid crystal display unit. There is provided an optical film characterized by containing cellulose ester (A), at least one ester plasticizer (B) selected from among an ester plasticizer from a polyhydric alcohol and a monocarboxylic acid and an ester plasticizer from a monohydric alcohol and a polycarboxylic acid, at least one stabilizer (C) selected from among a phenolic stabilizer, a hindered amine stabilizer and a phosphorus stabilizer, and hydrogen bonding solvent (D).