Novel hyperbranched polymer, poly[bis(diethylene glycol)benzoate] capped with a 3,5-bis[(3',6',9'-trioxodecyl)oxy]benzoyl group (poly-Bz1a), was prepared, and its polymer electrolyte with LiN(CF3SO2)(2), poly-Bz1a/LiN(CF3SO2)(2) electrolyte, was all evaluated in thermal properties, ionic conductivity, and electrochemical stability window. The poly-Bz1a/LiN(CF3SO2)(2) electrolyte exhibited higher ionic conductivity compared with a polymer electrolyte based on poly[bis(diethylene glycol)benzoate] capped with an acetyl group (poly-Acla), and the ionic conductivity of poly-Bz1a/LiN(CF3SO2)(2) electrolyte was to be 7 x 10(-4) S cm (-1) at 80 degreesC and 1 x 10(-6) S cm(-1) at 30 degreesC, respectively. The existence of a 3,5-bis[(3',6',9'-trioxodecyl)oxy]benzoyl group as a branching unit present at ends in the base polymer improved significantly ionic conductivity of the hyperbranched polymer electrolytes. The polymer electrolyte exhibited the electrochemical stability window of 4.2 V at 70 degreesC and was stable until 300 degreesC.