The polymer electrolytes with various compositions of Polyacrylonitrile/N-N Dimethylformamide (DMF)/Lithiumtetrafluoroborate (LiBF4) are synthesized by solution casting technique. The free standing, clear and transparent 60-80 micron thick films are formed. The promising structural and complexation changes in polymer electrolytes have been explored by X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) techniques. The thermal properties of all solid polymer electrolytes (SPE) were studied by Thermo gravimetric Analyzer (TGA) and Differential Thermal Analyzer (DTA). The electrical properties, i.e., ionic conductivity of solid polymer electrolytes has been measured as a function of temperature and composition. A Polymer membrane for 3 wt. % of salt has a conductivity of 3.06x10-4 mScm-1 at room temperature and 1.53x10-3 mScm-1 at 358K. The conductivity values increased with increase in temperature and offered an ionic conductivity of the order of 10-3 mScm-1 at temperatures 358K. Activation energy, enthalpy and entropy values are determined for all polymer complexes.