The present invention addresses the problem of providing a method for improving the solubility of a slightly soluble substance, said method being capable of enhancing the solubility of substantially all slightly soluble substances. This method comprises covering the surfaces of particles of a slightly soluble substance with fine particles of a calcium compound and a pH regulator and/or a surfactant through the application of a mechanical energy, said calcium compound including calcium phosphate, calcium carbonate and so on.
