Abstract: In order to improve the decontamination of neptunium in 2D extractor for uranium purification cycle, the oxidation conditions of Np(Ⅳ) and the effect of the pretreatment on the stability of Np(Ⅴ) have been studied. The results show that in 0.2mol/L nitric acid feed solution, 97% Np(Ⅳ) can be oxidized to Np(Ⅴ) or Np(Ⅵ) within 2h at 85℃. During the pretreatment, the ionic strength and the concentration of hydrazine has little influence on the stability of Np(Ⅴ). The concentration of Np(Ⅳ) increases with the temperature，pretreatment time and acidity.