To provide an electrolyte for a polymer battery having a high flexibility of design, in addition to high safety, and to provide a polymer battery equipped with the electrolyte for polymer battery.

This electrolyte for a polymer battery is prepared by heating an electrolyte composition comprising a phosphazene compound, tetralkylthiuram disulfides and a support electrolyte at 60°C or higher. This polymer battery is equipped with the electrolyte for a polymer battery, a positive electrode and a negative electrode. Since the phosphazene compound in the electrolyte composition is copolymerized by heating in the electrolyte for a polymer battery, electrolyte leakage will not occur.