PROBLEM TO BE SOLVED: To provide methods of producing a nanoparticle of a pteridine derivative, such as folic acid, which has a small particle diameter and in which temporal aggregation is suppressed.SOLUTION: A method of producing α-glucosylrutin-containing pteridine derivative nanoparticles comprises a step of making a particulate composition with a median diameter of 1000 nm or less (preferably 100 nm or less) by the grinding treatment of a mixture containing 0.9 pt.wt. or more of α-glucosylrutin, such as α-mono-glucosylrutin, with respect to 1 pt.wt. of a pteridine derivative, such as folic acid. As the grinding treatment, for example, wet grinding treatment using bead mill is preferable.SELECTED DRAWING: None
