An oxidation process for an article to be treated in which, by generating ozone with a high concentration, a high treatment rate is achieved. In particular, an oxygen-containing fluid is irradiated with a vacuum ultraviolet rays emitted from a dielectric barrier discharge lamp in which xenon gas is encapsulated, producing a photochemical reaction from which ozone and an activated oxygen result. By causing this ozone and activated oxygen to contact the surface of the article to be treated, the surface of the article is oxidized. An even higher treatment rate can be achieved by generating the activated oxygen with the simultaneous use of a far ultraviolet ray source, thereby increasing the activity of the activated oxygen. Advantageously, the oxidation of the article to be treated with the vacuum ultraviolet rays and far ultraviolet rays is performed in accordance with the relationship:(p.times.d)/(1+I.sup.1/2)=0.33where I is a radiation density (mW/cm.sup.2) of the far ultraviolet rays on a surface of the article to be treated in which there is no light absorption between the far ultraviolet ray source and the surface of the article to be treated, d is a shortest distance (cm) of passage of the vacuum ultraviolet rays emitted from the dielectric barrier discharge lamp to the surface of the article to be treated, and p is an oxygen partial pressure (atm) of the oxygen-containing gas, which is present between the dielectric barrier discharge lamp and the article to be treated.