Provided is a method for increasing the solubility of a poorly-soluble substance used in pharmaceutical products, veterinary pharmaceutical products, quasi-drugs, cosmetic products, food products, agricultural chemicals, and the like, without using large amounts of additives. This is a method for improving aqueous solubility, which comprises coating the surface of the particle of a poorly-soluble substance used in pharmaceutical products, veterinary pharmaceutical products, quasi-drugs, cosmetic products, food products, agricultural chemicals, and the like, with microparticles of a calcium compound such as calcium phosphate or calcium carbonate.
