An investigation of iodine absorption on ion exchange resins in aqueous electrolyte solutions has been performed. For I- and I ions, the distribution coefficients are inversely proportional to the electrolyte concentration in solutions, whereas the adsorption of HIO with ion exchange resins is independent of electrolyte concentration in solutions. The mechanism of HIO adsorption is believed to be surface matrix adsorption rather than the ion exchange process. The distribution coefficients for HIO measured at both 20 and 56°C are nearly constant, whereas the coefficients for I- and I ions are approximately a factor of 100 smaller at the higher temperature. The distribution coefficients for I- ions in water are generally on the order of 104, which is approximately three to five times larger than that for I- ions. The half-time of the exchange reaction for I ions with the strong acid resin in water at 20°C is ∼50 s, compared to ∼90 s for I ions. Some experimental data obtained in an operating boiling water reactor have also been reported.