Knowledge of antimony redox kinetics is crucial in understanding the impact and fate of Sb in the environment and optimizing Sb removal from drinking water. The rate of oxidation of Sb(III) with H2O2 was measured in 0.5 mol L-1 NaCl solutions as a function of [Sb(III)], [H2O2], pH, temperature, and ionic strength. The rate of oxidation of Sb(III) with H2O2 can be described by the general expression:  −d[Sb(III)]/dt = k[Sb(III)][H2O2][H+]-1 with log k = −6.88 (±0.17) [k:  min-1]. The undissociated Sb(OH)3 does not react with H2O2:  the formation of Sb(OH)4- is needed for the reaction to take place. In a mildly acidic hydrochloric acid medium, the rate of oxidation of Sb(III) is zeroth order with respect to Sb(III) and can be described by the expression −d[Sb(III)]/dt = k[H2O2][H+][Cl-] with log k = 4.44 (±0.05) [k:  L2 mol-2 min-1]. The application of the calculated rate laws to environmental conditions suggests that Sb(III) oxidation by H2O2 may be relevant either in surface waters with elevated H2O2 concentrations and alkaline pH values or in treatment systems for contaminated solutions with millimolar H2O2 concentrations.