Abstract: Under the condition of (25±0 2) ℃, the balance time for the precipitating reaction of plutonium(Ⅳ) oxalate and the solubility of plutonium(Ⅳ) oxalate precipitate in mixed solution of HNO 3 H 2C 2O 4 with different concentration have been studied. 1 mL of 1 mol/L H 2C 2O 4 is added into the 9 mL solution containing 0.9 mg/mL Pu(Ⅳ) and 4.0 mol/L HNO 3. After mixing for 5 min, the yellow green precipitate of plutonium(Ⅳ) oxalate is obtained. Standing for more than 22 h, the precipitating reaction reaches equilibrium. The solubility of plutonium(Ⅳ) oxalate precipitate in the mixed solution of HNO 3 H 2C 2O 4 is increased with the concentration increasing of H 2C 2O 4 and decreased with the concentration increasing of HNO 3 in the mixed solution. In the TRPO process, The solubility of plutonium(Ⅳ) oxalate precipitate in the stripping solution of Pu and Np(mixed solution of 0.56 mol/L HNO 3 0.3 mol/L H 2C 2O 4)≈110 mg/L, but in hot cell experiment of TRPO process, the concentration of Pu(Ⅳ) in the solution is less than 100 mg/L. Therefore plutonium(Ⅳ) can not be precipitated in the solution.