Disclosed is a sulfur-based electrode active material with which a nonaqueous electrolyte secondary battery that has a large capacity and exhibits less deterioration of the cycle characteristics can be obtained even when an electrode is employed in which the sulfur-based electrode active material is used as an electrode active material and an aluminum foil is used as a current collector. Also disclosed is a method for producing an organosulfur electrode active material, including a step of obtaining an organosulfur compound by heat-treating an organic compound and sulfur and a step of treating the organosulfur compound with a basic compound. The organosulfur compound is preferably sulfur-modified polyacrylonitrile, and the basic compound is preferably ammonia. The organosulfur compound may be treated with the basic compound after the organosulfur compound is ground, or may be ground in a medium that contains the basic compound.