Clear evidence for encaging guest mols. in a host material was obtained for FAU-type zeolite contg. fluorescein (FL) as a guest by employing the luminescence-quenching phenomenon of FL with C60. Whereas fluorescence of FL mols. adsorbed on the outer surface of the zeolite was effectively quenched as well as that in a homogeneous soln., that of the most FL mols. in the cages of the zeolite did not suffer from quenching by C60, giving clear evidence that FL mols. are located in the inner cages, which are inaccessible to C60. Only the fluorescence of the FL mols. located in the cages in the outermost unit cells of the zeolite was partially quenched. This partial quenching can be understood by considering the structure of the zeolite and the crit. distance of electron transfer inducing the fluorescence quenching.