Provided are a lithium secondary battery with suppressed decomposition of an electrolytic solution, and a preparation method thereof. The lithium secondary battery includes a current collector, a cathode and an anode having each active material layer formed on the current collector, and a polymer electrolyte interposed between the cathode and the anode. In the lithium secondary battery, a fluorine resin film is formed on at least one surface of the active material layers of the cathode and the anode. A fluorine resin exists in pores between constituents contained in at least one active material layer of the cathode and the anode. The polymer electrolyte is a polymerized product of a crosslinking monomer and an electrolytic solution including a lithium salt and an organic solvent. Also, a porous membrane made of an insulating resin is interposed between the cathode and the anode.