The present invention provides norbornene-based copolymers for which one monomer is at least selected from a group consisting of norbornene and dicyclopentadiene, and the other from norbornene-based comonomers of Formula 1 shown below: ##STR00001## In Formula 1, R.sub.1, R.sub.2 and a are defined in this specification.The present invention provides insulating elements for multi-chip packages and antireflection films for the exposure process of semiconductor fabrication using said norbornene-based copolymers. Norbornene-based copolymers according to the present invention have low dielectric constant as well as high thermal stability and excellent solubility to various organic solvents.