The intracrystalline diffusivities of benzene within porous materials in isopropanol solution were measured by the conventional constant volume method. The diffusivities within mesoporous silicas in isopropanol solution were smaller than those in cyclohexane Solution. This means the effective pore diameter for the benzene diffusion in the presence of isopropanol is small, because isopropanol are preferentially adsorbed on the pore surface with silanol group due to the hydrophilic affinity.