Series of gel electrolytes based on thermoplastic polyurethane (PU) with different organic additives were prepared and studied. Structural characterization was carried out by differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results showed that propylene carbonate (PC), NN-dimethylformamide (DMF), polyethyleneglycol 400 (PEG400), and glycerol played roles of plasticizers and were miscible with soft-segment in PU matrix, which led to increase of the polymer segmental mobility, which in turn led to decrease of glass transition temperature (T-g), while, diethyl carbonate (DEC) and diethylene glycol dimethyl ether (DGDE) showed no effectiveness of plasticizers. Ionic conductive properties of the electrolytes, examined by complex impedance analyzer, showed that ionic conductivities of the samples increased with the increase of organic additive content, and the sample with PEG400 as organic additive showed an ionic conductivity of 1.8 X 10(-5) S cm(-1) at room temperature. (C) 2003 Wiley Periodicals, Inc.