This study investigates the adsorption behaviors of chlorate and chlorite by MIEX resin, and determines the optimal conditions for the removal rate by utilizing response surface methodology. The chemical properties of the solution, such as pH, coexistent anions and ion strength, have great influences on the adsorption of chlorate and chlorite. The adsorption capacities of chlorate and chlorite by MIEX are 525 and 398 mg L⁻¹, respectively. When the pH is close to neutral, the removal rate of chlorate and chlorite on MIEX is the best. Sulfate radicals have a damaging influence on the adsorption of chlorate and chlorite on MIEX, leading to a low adsorption capacity. The initial adsorption kinetics of chlorate and chlorite adsorption on MIEX follows the intra-particle diffusion-controlled adsorption. The Box–Behnken design method is successfully used to establish a quadratic polynomial mode for predicting the removal efficiency of chlorate and chlorite, which is composed of three variables (adsorbent dosage, reaction time and initial concentration). The optimal removal conditions are: dosage 6.67 mL L⁻¹, reaction time 45.26 min, initial concentration 3.08 mg L⁻¹ for chlorate; and dosage 9.62 mL L⁻¹, reaction time 46.36 min, initial concentration 3.04 mg L⁻¹ for chlorite. According to the results, the adsorbent dosage has a strong interaction with the chlorate or chlorite concentration and reaction time, which has a significant impact on the optimization of the chlorate and chlorite removal process using MIEX. According to FTIR spectra, the adsorption mechanism for chlorate and chlorite is anion exchange.