The temperature dependence of the reactions of the primary water radiolysis radicals, O˙^–, e^–_aq and ˙OH with IO₃^– has been determined using electron pulse radiolysis and absorption spectroscopy. The transient growth of the IO₄˙^2– species at 360 nm, formed by the oxide radical addition to iodate, was used to determine its reaction rate constant of (1.66 ± 0.04)× 10⁹ dm³ mol^–1 s^–1(22.1 °C), with a corresponding activation energy of 14.60 ± 0.67 kJ mol^–1. The equivalent values for hydrated electron reaction with iodate, obtained by directly monitoring the e^–_aq decay at 700 nm were (5.49 ± 0.15)× 10⁹ dm³ mol^–1 s^–1(21.5 °C) and 8.86 ± 0.26 kJ mol^–1, respectively. Arrhenius parameters for the reaction of the hydroxyl radical with iodate were determined using SCN^– competition-kinetics and computer simulation, to give a rate constant of (1.08 ± 0.48)× 10⁵ dm³ mol^–1 s^–1(22.0 °C) and activation energy of 26.5 ± 2.8 kJ mol^–1.