A cylindrical lithium secondary battery that is resistant to breakage of the porous heat-resistant layer and therefore excellent in both safety and battery characteristics. The cylindrical lithium secondary battery includes: a battery can having a bottom, a side wall, and an open top; an electrode assembly; a non-aqueous electrolyte; and a sealing plate covering the open top of the battery can that accommodates the electrode assembly and the electrolyte. The electrode assembly includes a strip-like positive electrode and a strip-like negative electrode that are wound together with a porous heat-resistant layer and a separator interposed between the positive and negative electrodes. The thickness A of the porous heat-resistant layer and the thickness B of the side wall of the battery can satisfy the relation: 0.005.ltoreq.A/B.ltoreq.0.1.