Abstract: The present invention relates to a technology for treating radioactive liquid waste containing a hardly degradable compound, and more specifically, to a technology for treating radioactive liquid waste containing a material such as an organic decontamination agent, an inorganic decontamination agent, liquid scintillation counter liquid waste, and the like generated at nuclear power plants, nuclear facilities, facilities at which radiation (radioactivity) is used, and the like. The method for treating radioactive liquid waste of the present invention includes adding two or more selected from the group consisting of a metal ion, an oxidizing agent, air, oxygen, or nitrous oxide, and a semiconductor to radioactive liquid waste to prepare a pre-treatment solution, and irradiating the pre-treatment solution with radiation.