Composite polymer electrolytes composed of poly(ethylene oxide) (PEO), BaTiO3 as a ceramic filler, LiN(CF3CF2SO2)2 as a lithium salt, and hyperbranched polymer (HBP) (poly[bis(triethylene glycol)benzoate] capped with an acetyl group) as a platicizer were examined as the electrolyte for all solid-state lithium polymer batteries and the ionic conductivity was optimized. The optimized 90wt.% [(80wt.% PEO–20wt.% HBP)12(LiN(CF3CF2SO2)2)]–10wt.% BaTiO3 electrolyte, where the PEO with Mn of 60×104, HPB with Mn of 15,000, and BaTiO3 with a particle size of 0.5μm were used, showed the ionic conductivity of 1.3×10−4 S/cm at 30°C and 1.6×10−3 S/cm at 80°C, respectively. The optimized composite polymer electrolyte has an electrochemical stability window of 4.0V and also it was stable until 307°C under air. Interfacial stability of the LiN(CF3CF2SO2)2-based composite polymer electrolyte for a lithium metal electrode was found to be better than that of LiN(CF3SO2)2-based one.