The invention relates to a method and apparatus for treating waste material including organic components and radioactive agents. According to the invention, the method comprising steps: the waste material including organic components and radioactive agents is gasified at temperature between 600-950 DEG C in a reactor to form a gaseous material; the gaseous material is cooled so that temperature is between 300-500 DEG C after the cooling; and solid fraction including radioactive agents is removed from the gaseous material in a gas cleaning step, in order to form a treated gaseous material. Further, the invention relates to a product gas.