Concerning decontamination of a radioactive liquid waste which includes seawater and nuclides from irradiated fuels and activated materials, the in-situ generation of metal hexacyanoferrates(II) by adding potassium hexacyanoferrate(II) and codecontamination of 134,137 Cs and some activation products were investigated. Transition metals arising from seawater in the waste solution precipitates in the preference order of Zn>Ni≥Co>Mn according to their solubility. The precipitate adsorbs 134,137 Cs, and decontamination will be attained by the following sedimentation with a polymer and filtration, as an example. Decontamination factor of activated products, 60 Co and 54 Mn, is dependent on concentration of hexacyanoferrate(II) in the solution.