The present invention relates to a polymer electrolyte, a lithium secondary battery using the same, and a method for manufacturing the lithium secondary battery, wherein: an electrode assembly is formed by using a porous nanofiber web as an electrolyte matrix; an organic electrolyte having a mixture of a gel polymer-forming monomer and a polymerization initiator is injected, and a gel polymer electrolyte is formed by polymerization; and the porous nanofiber web is maintained in a web form such that stability can be increased by preventing a short circuit between a cathode and an anode. The polymer electrolyte, according to the present invention, comprises: the porous nanofiber web which is provided with a plurality of nanofibers; and a gel polymer portion which is impregnated into the porous nanofiber web, wherein the gel polymer portion is formed by polymerizing the gel polymer-forming monomer after a non-aqueous organic solvent, a solute of lithium salt, and the organic electrolyte having the gel polymer-forming monomer and the polymerization initiator have been impregnated into the porous nanofiber web.