With regard to tritiated contaminants, effective and simple dry decontamination method using ozone gas were proposed. By the treatment in ozone gas of 400 ppmv at 400 K, in the cases of stainless steel, the decontamination efficiencies of over 99 % were obtained for 1 hour, and the decontamination efficiencies of aluminum were 80–86 %. By the treatment of ozone gas, the quantity of the carbon atom on the surface and in inside layer were decreased, and the oxidation on the surface and in inside was proceeded, which may be assumed and expected that the recombination, release and diffusion to the surface of tritium are prevented by a rigid oxide layer generated.The ozone gas treatment is easy to use and apply in practice with a simple and safe operation. Furthermore, gas-phase decontamination technology has many advantages over conventional wet methods, in particular, its simple control processes and small secondary waste. The proposed decontamination technology has the sufficient ability and potential to simplify a decontamination operation and reduce the large volumes waste.