Provision of a stable ±-lipoic acid. A method for producing ±-lipoic acid nanoparticles, the method comprising the steps of: preparing an aqueous dispersion liquid containing ±-lipoic acid and a nonionic surfactant； adding a divalent metal salt into the aqueous dispersion liquid, wherein the divalent metal salt is a divalent metal halide, a divalent metal acetate or a divalent metal gluconate； and adding an alkali metal carbonate or an alkali metal phosphate into the aqueous dispersion liquid which has been added with the divalent metal salt, thereby forming ±-lipoic acid nanoparticles.
