A new interesting series of linear, unsaturated copolyesters containing cyclopentanone moiety in the main chain were synthesized by interfacial polycondensation of a mixture containing one mole of both monomeric units 2,5-bis (4-hydroxybenzylidene) cyclopentanone (Ia) and 2,5-bis (4-hydroxy-3- methoxybenzylidene) cyclopentanone (Ib) together with two moles of different acid chlorides. The yield and the values of reduced viscosity of the copolyesters were found to be affected by the kind of organic phase, contribution of benzyltriethylammonium chloride as a catalyst, the quantitative ratio of organic to aqueous phase, concentration of hydrogen chloride acceptor and time of addition of the acid chloride. The resulting copolyesters were characterized by elemental and spectral analyses. Moreover, the various characteristics of the various types of prepared copolymers including: solubility, viscosity, X-ray diffraction analysis, DSC and TGA were determined and discussed. The electrical properties of the copolyesters were tested and the morphology of selected examples of the copolyesters was examined by scanning electron microscopy.