Abstract: The kinetics of the reduction of Np(Ⅵ) by methyl p-hydroxy-benzoate has been investigated with the method of TTA-extraction. The rate equation is deduced as follows:-dNp(Ⅵ)/dt = k NpO2 2+ p-HBAMEH+-1. A mechanism is suggested with the electron transfer to Np (Ⅵ) from the phenolic group as the rate-determining step . After comparing the kinetics data on the reduction of Np(Ⅵ) by a series of aromatic derivatives, a correlation is made between the rate constants of the reduction and the pKa values of the phenolic groups in those compounds.