Novel polymer electrolyte aimed for space-selective electrochromic imaging was prepared with poly(vinylbutyral) (PVB), poly(ethyleneglycole) (PEG2000) and tetrabutylammonium perchlorate (TBAP). A spreading of the electrochromic image is a shortcoming when the electrochromic image is space-selectively formed by electrochemical reaction. This is due to a cell formation between colored and uncolored parts through ionic conductor. In order to inhibit the spreading, it would be effective to apply a polymer electrolyte with very low ionic conductivity at room temperature to the imaging system. On this basis, the present electrolyte was designed to have large difference in ionic conductivity between high and low temperatures. Namely, this polymer electrolyte enables writing and erasing at high temperature due to high ionic conductivity, and the image is expected to be preserved without change at ambient temperature due to very low ionic conductivity. The thermal and conductive properties of the polymer electrolyte were analyzed. Further, space-selective electrochromic image was formed on the device with the present polymer electrolyte at 100°C, and was revealed to be stable without change for more than a week when the device was kept at 20°C.