Abstract: In order to explain the distribution of neptunium in 1B contactor, the kinetics of reaction between Np(Ⅵ) and dimethylhyoxylamine (DMHAN) as well as Np(Ⅴ) and DMHAN, Np(Ⅴ) and methylhydrazine (MMH) was studied. The reaction rate is much faster between Np(Ⅵ) and DMHAN/MMH than that between Np(Ⅴ) and DMHAN/MMH. The rate equation of the reaction between Np(Ⅵ) and DMHAN is obtained as -dc(Np(Ⅵ))/dt ＝ kc(Np(Ⅵ))c(DMHAN)/c^0.6(H⁺), and the apparent k is 289.8 (mol•L^-1)^-0.4•min^-1 at 25 ℃. The rate equation of the reaction between Np(Ⅴ) and DMHAN is -dc(Np(Ⅴ))/dt ＝ kc (Np(Ⅴ)) c (DMHAN) c (H⁺), and k is 0.023 6 (mol•L^-1)^-2 •min^-1 at 25 ℃. The rate equation of the reaction between Np(Ⅴ) and MMH is -dc (Np(Ⅴ))/dt ＝ kc (Np(Ⅴ)) c 0.36 (MMH) c (H⁺), and k is 0.002 2 (mol•L^-1)^-1.36 •min^-1 at 25 ℃. When the process is controlled by diffusion, the stripping rate equation for Np from 30%TBP/OK by DMHAN is obtained as -dc_a(Np(Ⅵ))/dt = k(V/S)c^0.5_o,0 (Np(Ⅵ)) •c_o^-0.14 (TBP) c_a^-0.32(NO₃^-), k is 2.29×10^-4(mol•L^-1)^0.96•cm^-1•min^-1 at 25 ℃, and dc_a(Np(Ⅵ))/dt = k(V/S)c_o,0^0.63(Np(Ⅵ)) c_o ^-0.27 (TBP)c_a^-0.34(NO₃^-), k is 6.24×10^-4(mol•L^-1)^0.98•cm^-1•min^-1 at 25 ℃. Based on these kinetic parameters, the stripping efficiency of Np in 1B contactor is calculated as 95%.