Disclosed is a method for producing a norbornene monomer composition, a norbornene polymer produced using the norbornene monomer composition, an optical film including the norbornene polymer, and a method for producing the norbornene polymer. The method includes reacting a reaction solution that contains cyclopentadiene, dicyclopentadiene, or a mixture of cyclopentadiene and dicyclopentadiene, an acetate compound, and a solvent so that a content of an exo isomer is 50 mol % or more. Variables such as a reaction temperature, a reaction time, a molar ratio between reactants, and addition of a solvent are controlled so that the exo isomer is contained in content of 50 mol % or more. Accordingly, it is possible to industrially produce an acetate norbornene addition polymer by using the acetate norbornene monomer composition containing the exo isomer in content of 50 mol % or more.