We fabricated an interpenetrating network type solid polymer electrolyte with a promising mono-comb type poly(siloxane-g-ethylene oxide) for lithium rechargeable battery. The ionic conductivity of the network polymer electrolyte was closed to 10−4 S/cm at near room temperature. Initial cycling result from LiNi0.8Co0.2O2/polymer electrolyte/lithium metal cell shows excellent cycling characteristics with no capacity fade in a solid electrolyte system. The new polysiloxane polymer electrolyte could be a promising system for large batteries that necessitate long life and inherent safety such as batteries for electric vehicle applications.