NOVELTY - A gel polymer electrolyte composition (C1) comprises a compound (C2) acting as a monomer for forming gel polymer by polymerization and having at least two double bonds at its end; an electrolyte solvent containing carbonate and linear saturated ester; an electrolyte salt; and a polymerization initiator.    USE - For forming a gel polymer electrolyte useful in an electrochemical device, including a lithium secondary battery (claimed); useful for rechargeable secondary batteries useful in the fields of cellular phones, camcorders, notebook computers, PCs and electric cars.    ADVANTAGE - The composition allows to prepare a gel polymer electrolyte capable of ensuring excellent mechanical strength and improving various performances of battery such as room/low temperature characteristics and rate capacity. The monomer can conduct polymerization reaction in various ways since it has at least double bonds at its end. As a result, a polymer matrix with a planar structure and/or a net structure may be formed, and also mechanical strength of the gel polymer electrolyte may be improved. In addition, carbonate and linear saturated ester are mixed as an electrolyte solvent, and this electrolyte solvent has a low viscosity. The linear saturated ester has a high impregnation rate for electrode or separator, so it may improve ion conductivity inside a battery. Also, the electrolyte solvent may prevent deterioration of battery performance caused by shrinkage of electrolyte at a low temperature since it has a low freezing point. Thus, the composition improves various performances of battery such as room/low temperature performance and rate capacity of a battery. The gel polymer electrolyte has excellent electrochemical stability, excellent mechanical strength and excellent lithium ion conductivity since a compound having at least two double bonds at its end is used as a monomer for forming gel polymer by polymerization, and an electrolyte solvent is made by mixing carbonate and linear saturated ester. In addition, a secondary battery including the gel polymer electrolyte can improve various performances such as room/low temperature characteristics, and rate capacity.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a gel polymer electrolyte (E1) formed by polymerizing the gel polymer electrolyte composition (C1); and    (2) an electrochemical device comprising a cathode, an anode, and the gel polymer electrolyte (E1).