Provided are a polymer electrolyte, a lithium secondary battery using the same, and a manufacturing method thereof, in which a gel polymer electrolyte is formed from a monomer for forming a gel polymer by a rapid polymerization reaction, when using a porous nanofiber web as an electrolyte matrix, and injecting an organic electrolytic solution formed by mixing the gel polymer forming monomer and a polymerization initiator, to induce an addition polymerization reaction, but the porous nanofiber web maintains a web-like shape. The polymer electrolyte includes: a separator made of a porous nanofiber web having a plurality of nanofibers; and a gel polymer portion impregnated in the porous nanofiber web. the gel polymer portion is formed by impregnating an electrolytic solution containing a non-aqueous organic solvent, a lithium salt solute, a gel polymer forming monomer, and a polymerization initiator in the porous nanofiber web and polymerizing the gel polymer forming monomer.