Catalytic oxidation of naphthalene in moist acetic acid solutions has been studied. The catalyst used was a silica-supported palladium which works in cooperation with the Cu+/Cu2+ redox couple. Products were 1-naphthol, 1,4-naphthoquinone and (E)-2-formylcinnamaldehyde with a total yield of more than 78% in which naphthoquinone shared 40%. Reaction mechanism has been discussed in comparison with that of benzene.