Abstract: The sorption behavior of ¹²⁵I^- on Gaomiaozi bentonite was studied as a function of pH, ionic strength, temperature and solid-to-liquid ratio with the method of batch sorption experiments. ¹²⁵I^- sorption on Gaomiaozi bentonite is shown to be sensitive to pH and ionic strength. The sorption of ¹²⁵I^- is negligibly small under neutral and alkaline conditions, while with the decrease of pH, the sorption increases rapidly until the maximum sorption appeares at pH=2.0, and with the pH decreases, the sorption rapidly decreases. It is found that the maximum equilibrium sorption constant of ¹²⁵I^- on bentonite appeares under the condition of pH=2.0 at the background electrolyte concentration of 0.10 mol/L NaClO₄, which is approximately 92 mL/g at T=298 K. The pH PZC of bentonite is about 9.5 and the pH PZC of montmorillonite is about 10.5 from the results of acid-base titration. Temperature has little effect on the sorption of iodine on Gaomiaozi bentonite and Freundlich isotherm model is more suitable to describe sorption of iodine on Gaomiaozi bentonite at different temperatures.