Spherical mesoporous silica was prepared by dispersing tetrabutoxysilane (TBOS) in an alkaline solution into which a cationic surfactant had been dissolved. The spherical mesoporous silica was prepared within the limited concentration regions of the surfactant. The diameter of the spherical mesoporous silica was about 500 mm, and the BET specific surface area was above 1000 m 2 g À1 . Within the as-synthesized spherical mesoporous silica, phenol and some organic compounds in aqueous phase were solubilized into the hydrophobic free space consisting of the hydrocarbon group of surfactants. The extent of solubilization was correlated with equilibrium concentration in aqueous phase by a Langmuir-type equation. The maximum solubilization for phenol was proportional to the BET specific surface area of the calcined spherical mesoporous silica. For some organic compounds maximum solubilization was directly proportional to a hydrophobic index ofthe organic compound, log (P OW ), where P OW is the distribution coefficient between the octanol and water phases.