Wet oxidations of naphthalene were carried out in autoclaves lined with Hastelloy-C, SUS-316, and Teflon. Naphthalene was almost completely converted at 393 K using the stoichiometric concentration of hydrogen peroxide aqueous solution, i.e., 0.2 mol L-1, in an autoclave lined with Hastelloy-C, whereas it was converted under excess oxygen gas, i.e., 2 MPa, over 500 K. Alloy liners of autoclaves showed clearly catalytic performances for wet oxidation using hydrogen peroxide. The order of activity was Hastelloy-C > SUS-316 > Teflon, which depended on the activating abilities for hydrogen peroxide. The main products were carbon dioxide and organic acids, such as phthalic acid and formic acid. The order of catalytic activities of liners made of various pure metals and alloys for the wet oxidation of naphthalene was speculated to be as follows: Pt, Fe > Cu, Hastelloy-C > Ni, Ag, SUS-316 > Al, Sn (= Teflon) > Ti > Mo.