New nateglinide crystals, i.e. nateglinide A-type crystals (main peaks in powder X-ray diffraction: 4.4°, 5.2°, 15.7°, 18.5°(2θ)), M-type crystals (main peaks in powder X-ray diffraction: 6.0°, 14.2°, 15.2°, 18.8°(2θ)) and P-type crystals (main peaks in powder X-ray diffraction: 4.8°, 5.3°, 14.3°, 15.2°(2θ)), can be produced by dissolving nateglinide in a solvent in which nateglinide is highly soluble and then adding a solvent in which nateglinide is difficultly soluble or, alternatively, by dissolving nateglinide in a mixed solvent composed of a solvent in which nateglinide is highly soluble and another solvent in which it is difficultly soluble, cooling the nateglinide solution to form crystals, filtering the mixture and drying the crystals at a specified temperature.