Poly(ethylene terephthalate-co-ethylene naphthalate) (PETN) hybrid films with four different organo-clays have been compared in terms of their thermal stabilities, mechanical properties, and morphology. Hexadecylamine-montmorillonite (C-16-MMT), dodecyltrimethyl ammonium-MMT (DTA-MMT), Cloisite 25A, and Cloisite 30A were used as organo-clays. In hybrid, Cloisite 25A was exfolated and dispersed homogeneous into the copolyester matrix. We found that the addition of only a small amount of organo-clay was enough to improve the thermal stabilities and mechanical properties of PETN/clay hybrid films.