Photoreaction and light absorption of dimethyl sulfide (DMS)-O-3 complex isolated in a cryogenic neon matrix were investigated by FTIR and visible-light absorption spectroscopy. Although visible light does not induce photoreaction for either monomer, a photoreaction to produce dimethyl sulfoxide (DMSO) was observed to occur upon the red light (700-740 nm) irradiation. New electronic absorption bands peaking at 470 and 600 nm due to DMS-O-3 complex appear in a visible spectral region, which are responsible for the photooxidation of DMS to DMSO.