The adsorption of a cationic luminescence probe, tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+)), into a mesoporous silica was investigated in order to understand the nature of mesoporous silicas as immobilizing media for organic guest species. The adsorption of the probe into the mesoporous silica was conducted by the reaction using a dimethylformamide solution of [Ru(bpy)(3)](2+) chloride. The adsorbed amount of [Ru(bpy)(3)](2+) was controlled by changing the concentration of the solutions. When the samples were dehydrated, the adsorbed [Ru(bpy)(3)](2+) ions aggregated to cause self-quenching of the luminescence. The luminescence was intensified dramatically upon hydration of the samples, indicating that the aggregated [Ru(bpy)(3)](2+) ions were dispersed in the mesopore to suppress the self-quenching.