Abstract: Formohydroxamic acid (FHA) is a new saltless reagent which may be used in the reprocessing of spent nuclear fuel. This paper reports the study on the γ radiation stability of FHA by ultraviolet-visible spectrophotometry, as well as the effect of nitric acid and monomethylhydrazine (MMH) on radiation stability of FHA. The results show that the radiation stability of FHA in aqueous solution increases with the concentration of FHA when the doses are from 10 to 1000 kGy, but decreases with the dose rising. In HNO₃-0.2 mol/L FHA solution, the radiation stability of FHA slightly increases when the concentration of HNO₃ is 0.2 mol/L, but decreases when the concentration of HNO₃ is not less than 0.5 mol/L. In MMH-1.0 mol/L HNO₃-0.2 mol/L FHA solution, the radiation stability of FHA increases with the concentration of MMH.