Composite electrolytes comprised of thermoplastic polyurethane (TPU) with polyacrylonitrile (PAN) were investigated. Differential scanning calorimetry (DSC) and impedance spectroscopy were used to monitor the changes in the thermal characteristics and bulk conductivity of the composites due to the amounts of PAN in the composite. Fourier transform infrared spectroscopy (FTIR) was employed to identify the modifications in molecular interactions associated with TPU. The deconvolution of spectral bands associated with C=O and the NH group of TPU and the C=N group of PAN was utilized to obtain such information. The bulk conductivity of the composites with different PAN content was determined, and the influence of PAN on that was brought out. The effects of temperature and lithium salt concentration on conductivity of the composites were analyzed with respect to TPU. The conductivity changes were correlated through DSC and FTIR results.