A series of thermotropic random copolyesters was prepared by the reaction of ethoxydiethylene-oxyhydroquinone and ethylene glycol with terephthaloyl chloride. The purpose of this study was to investigate the effect of the flexible pendent oxyethylene group on the thermal and liquid crystalline (LC) properties of the copolyesters which were designed to form composites at the molecular level with flexible coil polyesters such as poly(ethylene terephthalate). The LC copolymers were characterized by viscosity measurements, elemental analysis, thermogravimetry (t.g.a.), d.s.c. and polarizing microscopy. The inherent viscosity as well as the temperature corresponding to the crystalline-nematic transition of the copolyesters decreased with increasing ethylene glycol content up to 60 mol% content. Beyond this composition, the viscosity values levelled off and there was an increase in the temperatures corresponding to the melting transitions. Polarizing microscopy studies revealed that the polymer melts were anisotropic and developed a nematic LC texture. At compositions beyond 60 mol% of the flexible ethylene glycol unit, a biphasic melt consisting of a predominant isotropic phase was observed.