A process is provided that includes performing a high-temperature high-pressure hydrothermal treatment for a reaction liquid prepared as a mixture of an acylated inorganic fine particle precursor and an organic modifying agent that has a carboxyl group. Because the reaction liquid contains the acylated inorganic fine particle precursor in advance, the grain growth during the high-temperature high-pressure hydrothermal treatment can be suppressed. The process thus enables production of organic-modified inorganic fine particles of a size about the same as or even smaller than that before the high-temperature high-pressure hydrothermal treatment.
