Naphthalene adsorption profile on porous materials was studied using solid-state fluorescence spectroscopy. When naphthalene crystals were simply mixed with porous crystalline cellulose (PCC), excimer emission of naphthalene was observed after 1 min of mixing, suggesting a drastic change in the naphthalene molecular environment during the mixing procedure. For the naphthalene-octadesyl silane (ODS)-80A or naphthalene-ODS-2 systems, the changes in adsorption profiles and fluorescence spectral pattern of naphthalene were similar to those of the naphthalene-PCC system. The final amounts of naphthalene adsorbed to ODS-80A and ODS-2 were 0.05 and 0.024 g/g adsorbent, respectively, even though the two materials had comparable values of specific surface area. The relative emission intensity I/(excime)/I-monomer) in the ODS-80A system was higher than that in the ODS-2 system when compared at the same amount of naphthalene adsorbed. It was concluded that the pore size of porous materials affected the naphthalene excimer formation on the surface.