Abstract: In order to understand the chemical behavior of neptunium during the extraction process, the oxidation behavior of Np(Ⅴ) to Np(Ⅵ) in nitric acid solution and the extraction performance of Np(Ⅵ) by 30%TBP/kerosene was studied by single stage extraction. The experiment results indicate that the increasing of the concentrations of nitric acid and nitrous acid are in favor of the production of Np(Ⅵ). The reaction rate of Np(Ⅴ) to Np(Ⅵ) by oxidation increases with increasing the reaction temperature. The simulated experiment on the mixer-setter set indicates that the extraction ratio of neptunium in 1A extraction section is approximately 80% when the HNO₂ concentration in 1AX is 0.01 mol/L, the extraction temperature is 45 ℃ and the HNO₃ concentration in 1AF is 3.5 mol/L HNO₃.