In this study, structural, rheological and mechanical properties of cycloolefin copolymer/organoclay nanocomposite films were investigated in detail. A maleic anhydride grafted polyethylene was used as conventional compatibilizer. In a series of samples, poly(ethylene-co-1-octene) copolymer was also used as a secondary component in the sample formulations. Microstructural features of the samples and clay dispersion into the polymer phase were characterized by X-ray diffraction and scanning electron microscopy studies. Physical properties of the samples were examined with the melt rheology and dynamic mechanical analysis tests. Highly transparent films with the intercalated nanocomposite structure were successfully obtained. It was found that the poly(ethylene-co-1-octene) enhances the organoclay dispersion into polymer phase and the related physical properties of the samples. Some structural properties of the samples such as the critical volume fraction of organoclay (phi(p)) and aspect ratio (A(f)) were quantified with the experimental data obtained from the rheological and mechanical measurements. Critical volume fraction of organoclay at the percolation threshold was determined as 0.018 based on the rheological measurements. The Halpin-Tsai micro-mechanical model for composite materials was employed to determine dispersion of organoclay layers. The aspect ratio of organoclay tactoids was found to be about 12-15 based on the both rheological and micro-mechanical modeling.