Poly(ethylene-co-hexamethylene 2,6- naphthalate) copolyesters containing ethylene unit and hcxamethylene unit in polyester backbone were prepared by the melt polymerization and characterized by 1H-HMR spectroscopy. Intrinsic viscosity. glass transition temperature(Tg), crystallization temperature(Tcc), melting temperature(Tm) and decomposition temperature(Td) of copolyesters decreased with increase in the hexamethylene unit mol%. An increase in hexamethyl unit mol% resulted in less thermal stability of copolycsters.