Abstract: The reduction kinetics of TcO_4~-by Sn(Ⅱ) in basic medium is studied. The influence of the concentrations of TcO_4, Sn(Ⅱ), OH- and temperature on the reaction rate is investigated by extraction separation and liquid scintillation measurement for TcO_4 concentration. Experimental results show that TcO_4 is reduced to Tc(Ⅳ) by Sn(Ⅱ) and the stoichiometry of the reduction can be expressed as: 3Sn(Ⅱ)+2Tc(Ⅶ)3Sn(Ⅳ)+2Tc(Ⅳ). The reaction rate expression is obtained as: -dc(TcO_4)/dt=kc(TcO_4)c -0.478 (OH-)c 0.629 (Sn(Ⅱ)). The activation energy of the reaction is about 29.08 kJ/mol.