Abstract: The reaction kinetics between dimethylhydroxylamine (DMHAN) and Np(Ⅵ) in nitric acid media was studied by spectrophotometry. By investigating the influence of DMHAN concentration and acidity on the reaction, the reaction rate equation is obtained: -dc(Np(Ⅵ))/dt=kc(Np(Ⅵ))c(DMHAN)/c^0.6(H⁺), and the rate constant is 289.8(mol/L)-0.4/min at 25℃ and I=4.0mol/kg. The effects of ionic strength, c(U(Ⅵ)), and temperature were also investigated. The results show that the ionic strength and c(U(Ⅵ)) have no obvious effects on the reaction. The reaction activation energy was found to be 53.3 kJ/mol(25℃) by plotting the reaction rate constant against the reciprocal of reaction temperature. The negative activation energy implies that rising temperature will accelerate the reaction. Based on the above results, the reaction mechanism was explored.