The present invention uses a magnesium-based alloy which is excellent in mechanical workability to be formed thinner than conventional alloys. The present invention provides a lithium secondary battery comprising an electrode assembly and a non-aqueous electrolyte, both accommodated in a metal jacket, wherein the metal jacket is made of a magnesium-based alloy containing lithium in an amount of 7 to 20% by weight; and a metal layer or an insulating layer for preventing corrosion of the metal jacket is formed integrally with the metal jacket on the inner wall thereof.