The applicability of the Dreiding 2.21 and PCFF force fields to the prediction of properties of cyclo-olefin copolymers was evaluated. The initial performance of the force fields was only modest, and reoptimization of the force field parameters was required. The reoptimization was performed for the Dreiding 2.21 force field by fitting the force field to the potential energy curves of B3LYP/6-31G* calculations. The modifications to the force field resulted in a considerable improvement, bringing the calculated mechanical and thermal properties close to the experimental values. Experimental substructures for polymer fragments were obtained from the Cambridge structural database. Theoretical potential energy minima were found to be in good agreement with the experimental structural data.