Acetylation with acetic anhydride and alkylation with butylene oxide were applied to sugi (Cryptomeria japonica D. Don) veneers and blocks and the treated surfaces were evaluated for their photo-resistance using XPS (X-ray photo-electron spectroscopy) and colorimetry. Chemical modification treatments were expected to increase the weathering resistance of wood and the durability of weathering-resistant transparent type of coating films. Color changes on the chemically modified wood surfaces upon exposure to UV light were less conspicuous than those of untreated wood surfaces, but the photo-oxidation of modified wood surfaces, as estimated using XPS, was similar to that of untreated wood. Chemical modification did not increase the bonding strength or weathering resistance of transparent coating films.