Possibility of reduction and removal of heavy metal ions Ag+, Zn2+, Cu2+, and Co2+from water by irradiation of γ ray was investigated. No concentration change was found when aqueous solutions of the metal ions were irradiated with γ ray either directly, or after bubbling with He gas. On the other hand, the metal ions were reduced to lower oxidation states by the irradiation in the presence of Na2SO3. Precipitates were observed in all the irradiated solutions of 4 metal ions of Ag+, Zn2+, Cu2+, and Co2+. Ag+was found to be reduced to metallic Ag.