Abstract: It was found that in the nitric acid solution containing U(Ⅳ), hydrazine, Tc(Ⅶ) and Np(Ⅴ), Np(Ⅴ) was reduced to Np(Ⅳ) quickly. The main reason of the fast reduction of Np(Ⅴ) was due to Tc(Ⅳ), which was produced by the reduction of Tc(Ⅶ) in the presence of U(Ⅳ). The routing of Np in U/Pu separation stage was studied by tube cascade experiments and bench scale experiments at a miniature mixing settler set. The results show that nearly 67.7% of Np goes into 1BU in the presence of Tc in the 1AP, but approximately 27.0% of Np goes into the 1BU in the absence of Tc. The amount of Np going into 1BU increases with the reaction temperature and the concentration of Tc(Ⅶ) in 1AP.