The oxidation of thiourea by ferrate(V) (Fe(V)) has been studied as a function of pH in alkaline solution by a premix pulse radiolysis technique. The rate law for the oxidation of thiourea by Fe(V) was obtained as −d[Fe(V)]/dt=k 0{[H+]/([H+]+K5)}[Fe(V)][TU] where k0=4.40±0.08×105 M −1 s −1, pK5=10.1. The predominant reaction is between the protonated Fe(V) species, HFeO4 2− and thiourea. Thiourea reacts approximately 103 times faster with Fe(V) than it does with Fe(VI). The higher reactivity of Fe(V) with thiourea indicates that the oxidation by Fe(VI) may be enhanced in the presence of an appropriate one-electron reducing agent.