The preparation, the electrical and rheological properties as well as the electrochemical behavior of gel electrolytes made of (PC) electrolyte mixed with poly(methylmethacrylate) polymer (PMMA) as a stiffener are described. The addition of PMMA in various proportions to (M)‐PC electrolyte considerably increases the viscosity to reach for large amounts of PMMA, a solid rubber‐like material. On the other hand the conductivities at room temperature of these gels decrease very slightly and remain very close to the conductivity of the liquid electrolyte. Moreover, the electrochemical study of these materials shows a stability domain on Pt electrode between −3.55 V and +1 V (vs.Ag/Ag+). They behave like a liquid electrolyte. Differential scanning calorimetric data establish the thermal stability of these gels between −110 and +240°C after heat‐treatment and between −90 and +160°C before heat‐treatment. These results indicate that this type of electrolyte which is transparent in thin films is very promising for the realization of solid‐state electrochromic windows.