The present invention relates to a norbornene based addition polymer, and more particularly to an addition polymer of norbornene based monomers containing an ester group. The present invention provides a norbornene-ester based addition polymer having a molecular weight (Mn) larger than 20,000 and comprising a norbornene-ester based monomer comprising more than 50 mol % of exo norbornene-ester monomer as a repeating unit, a method for preparing the same, and an optically anisotropic film comprising the same. The norbornene-ester based addition polymer of the present invention is transparent, has a low dielectric constant, has good thermal stability and strength, leaves no unwanted materials when attached to metals or other polymers, and has good adhesivity, so that it can be used for optical films, retardation films, plastic substrate materials, transparent polymers such as POF or PCB, insulating materials, or insulating electronic devices such as PCB or insulating materials.