A new polyester, poly[ethylene 7-(N-pyrrolidinyl)-2,7-cycloheptadiene-1,2-dicarboxylate] and its lithium triflate complex have been successfully synthesized and characterized in detail. Solution studies (viscosity and electronic spectroscopy) were realized in two different solvent mixtures, dimethyl sulphoxide (DMSO)/dimethyl formamide (DMF) (1:1 v/v) and DMSO/p-chlorophenol (p-CP) (1:1 v/v). DMSO/p-CP was a better solvent mixture to obtain Li+ ion-doped polyester. FTIR spectra supported the complex formation. According to viscosimetric measurements the polymer was a low molecular weight polyester. In DTG analysis, the polymer decomposed by a multi-step process whereas two-step decomposition was observed for polymer-Li+ ion complex. The glass transition temperature of the polyester and its Li+ complex were determined as 345degreesC and 360degreesC respectively by means of DSC analysis.