The preparation of a new type of poly(ethylene oxide)‐polysiloxane hybrid (PEOS) with its application to the construction of solid‐state electrochromic devices was studied. The PEOS was given as a colorless and elastic membrane by condensation of a bis(silylpropyl) ether of oligo(ethylene oxide) and a polyalkoxysilane in the presence of LiClO4 (2–5 mole percent). The ionic conductivity reached 10−3 S cm−1 when PEOS was swollen with propylene carbonate by 160% in weight. A transparent‐type solid‐state electrochromic device composed of Prussian blue‐ and WO3‐normalcoated electrodes with PEOS was prepared, switching of which was slower by a factor of 1.5–2.0 as a function of half‐time of coloration and bleaching compared with the corresponding liquid‐type cell.