Abstract: Batch experiments were conducted to understand the main differences between Fe²⁺/PDS and Fe⁰/PDS systems during the degradation process of reactive brilliant blue KN-R. The effects of dosages of Fe²⁺, Fe⁰ and PDS, and the initial pH on KN-R degradation were investigated. In the Fe²⁺/PDS system, when the initial pH was set at 3.0, Fe²⁺ concentration was 1.0 mmol/L and PDS concentration was 2.0 mmol/L, the maximum degradation ratio was 96.55% after 180 minutes. The faster the pH or Fe²⁺ concentration increased, the worse the KN-R degradation decreased. However, in the Fe⁰/PDS system, pH and Fe⁰ dosage did not restrain the KN-R removal. The degradation ratio of KN-R was 90.53% after 180 minutes at pH=9.0, while it reached 94.35% within 50 min at Fe⁰ dosage of 448 mg/L. In the Fe²⁺/PDS and Fe⁰/PDS systems, PDS could improve the removal rate of KN-R remarkably. When the concentrations of PDS increased from 0.5 mmol/L to 8.0 mmol/L, the removal ratios increased from 47.25% and 57.00% to 100% in the Fe²⁺/PDS and Fe⁰/PDS systems, respectively. Kinetic analysis indicated that the degradation of KN-R followed a first order kinetics equation. Radical identification showed that SO₄^-· were the main radicals in the Fe²⁺/PDS and Fe⁰/PDS systems. In conclusion, the Fe⁰/PDS system was superior to the Fe²⁺/PDS system during the degradation process of KN-R.