A nonaqueous electrolyte secondary battery having an enhanced capacity and a long charge/discharge cycle life is disclosed. The nonaqueous electrolyte secondary battery comprises a positive electrode housed in a case and containing a chalcogen compound as an active material, a negative electrode arranged in the case such that a separator is sandwiched between the positive and negative electrodes and containing a carbonaceous material as an active material that absorbs and discharges lithium ions and a nonaqueous electrolyte contained in the case and prepared by dissolving 0.5 mol/l to 1.5 mol/l of electrolytic salt selected from the group consisting of LiPF.sub.6, LiBF.sub.4, LiAsF.sub.6 and LiCF.sub.3 SO.sub.3 in a solvent mixture comprising at least one first nonaqueous solvent selected from the group consisting of noncyclic carbonate, cyclic carbonate, .gamma.-butyrolactone and acetonitrile and at least one second nonaqueous solvent containing selected from the group consisting of 1,2-diethoxyethane, 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, 1,3-dimethoxypropane, diethylether and tetrahydrofurane, the amount of said second nonaqueous solvent in the solvent mixture being so determined that the mol ratio ([S]/[Li]) of the second nonaqueous solvent [S]to lithium ions [Li]is 0.5 to 3.