In this presentation the results of a study of a new solid polymer electrolyte based on poly(trimethylene carbonate), henceforth. designated as p(TMC), and lithium hexafluoroarsenate are described. Samples of electrolytes with different salt contents were prepared by solvent casting from tetrahydrofuran and characterized by conductivity measurements and thermal analysis using DSC and TGA. The salt content of these electrolytes was identified by the conventional notation based on the polymer/salt ratio. In accordance with this notation the value of n represents the number of ((C=O)OCH2CH2CH2O) units per lithium ion. The appearance and morphology of electrolyte samples with compositions of n between 4 and 80 was similar to that observed with electrolytes based on the same host polymer with other lithium salts. Over this composition range thin films of electrolyte were transparent, freestanding and completely amorphous.