Pyrene crystals were physically mixed with either porous crystalline cellulose (PCC) or octa decyl siryl silica-80TM (ODS). Solid-state fluorescence spectra of pyrene were analyzed to estimate the interaction between pyrene and porous materials. Pyrene monomer emission was observed at 398 Mn immediately after being mixed with PCC, while pyrene crystals showed only excimer emission at 475 nm, indicating that the pyrene molecules adsorbed onto the PCC surface in a short period. For the PCC system containing 1.0% pyrene, long-term storage caused an increase in the intensity of excimer-like emission peak at 477 nm accompanied by a decrease in the intensity of monomer emission peak at 398 nm. For the ODS system containing 1.0% pyrene, spectrometric changes were similar to those for the PCC system. In the process of interaction formation between pyrene and an additive, a two-step mechanism was proposed, i.e., the adsorption of pyrene molecules onto the surface of porous additives, and the formation of a ground state dimer of pyrene. The formation of dimeric pyrene could be associated with the surface polarity of additives.