Adsolubilization of 2-naphthol and naphthalene by cationic surfactant-adsorbed layers formed on titanium dioxides with or without a dodecyl chain was investigated, The cationic surfactants used were dodecyltrimethylammonium bromide and 1,2-bis(dodecyldimethylammonio) ethane dibromide (2RenQ), It was found that the adsolubilized amounts of 2-naphthol and naphthalene increase and reach a maximum and then decrease for both surfactants and titanium dioxides with or without the dodecyl chain, where in the absence of surfactants the incorporated amount of naphthalene on the titanium dioxide with the dodecyl chain is markedly large, The adsolubilized amounts of 2-naphthol and naphthalene were enhanced with the titanium dioxide with the dodecyl chain by adsorption of surfactants, in particular 2RenQ, The admicellar partitioning coefficients also showed that naphthalene is adsolubilized preferentially rather than 2-naphthol and the surface treatment with the dodecyl chain enhances the adsolubilization for two adsolubilizates.