Abstract: The kinetics of reaction between Pu(Ⅳ) and hydroxysemicarbazide (HSC) in nitric acid solution was studied. The rate equation is found to be: ：-d_c（Pu(Ⅳ)）/d_t=kc（Pu(Ⅳ））c^1.06（HSC）c^-0.43（H⁺）c^-0.58（NO₃^-）, wherek＝(11.8±1.1) （mol/L）^-0.046•s^-1 at 22.1 ℃ and the activation energy E_a＝(71.0±1.0) kJ/mol. Effects of c(HSC), c(H⁺), c(Fe³⁺), c(UO₂²⁺), ionic strength and temperature on reduction rate of Pu(Ⅳ) were investigated. The results show that Pu(Ⅳ) can be rapidly reduced to Pu(Ⅲ) by HSC under normal conditions. The reaction rate can be accelerated by increasing concentration of hydroxysemicarbazide or temperature, and decreasing concentration of HNO₃ or ionic strength. The influence of UO₂²⁺ and Fe³⁺ on reaction rate is negligible.