This invention is intended to improve the solubility and permeability of low-solubility drugs, including drugs hardly soluble in water, classified as Class 2 or 4 in accordance with BCS by modifying such drugs into S/W, S/O, or S/O/W preparations. The S/W, S/O, or S/O/W preparations of low-solubility drugs of this invention are prepared by a method for preparing a composite of a low- solubility drug and surfactant by introducing air or nonflammable gas into the gas phase in the upper portion of a liquid level of the dispersion, dissolution, and emulsification tanks, respectively, at a pressure of 1 to 10 atm.
