Abstract: The solubility of Pu (III) oxalate in the HNO_3-H_2C_2O_4 medium is determinedin the present work. Experimental results show that at different concentrations ofnitric acid the solubility of Pu (III) oxalate gradually decreases with the increasein the concentration of oxalic acid. Resultes also show that when the concentrationof nitric acid is less than 1 mol/l, the increase in the concentration of oxalicacid causes a gradual decrease in the solubility of the oxalate, which reaches aminimum and then increases with the addition of more oxalic acid. This is inter-preted in terms of the formation of oxalate complexes. At different concentrationsof oxalic acid, the solubility of Pu (III) oxalate increases with the increase inthe concentration of nitric acid to some extent. The elevation of temperatureresults in greater solubility of Pu(III) oxalate. The ionic strength was kept at I=2.3 except when the concentration of nitric acid is 3 mol/l, in which case I=3.3.