Provided are a method for producing organic material microparticles and a method for modifying organic material microparticles, whereby it becomes possible to improve the crystallinity of organic material microparticles or achieve the crystal transformation of the organic material microparticles while preventing the growth of the organic material microparticles in a solvent. A surfactant is added to a solvent that is capable of partially dissolving organic material microparticles, and then the organic material microparticles are reacted with the solvent. In this manner, it becomes possible to improve the degree of crystallization of the organic material microparticles or achieve the crystal transformation of the organic material microparticles without substantially altering the particle diameters of the organic material microparticles.
