The oxidation and removal of As(III) by commercially available micro-scale zero-valent iron (mZVI) was studied in aerated synthetic groundwater with initially 6.7 μM As(III) at neutral pH values. Batch experiments were performed to investigate the influence of ZVI and H₂O₂ concentrations on As(III) oxidation and removal. Oxidation and removal kinetics was significantly increased by increasing ZVI concentration or by adding H₂O₂ in micromolar concentrations slightly higher than that of initial As(III). Observed half-lifes for arsenic removal without added H₂O₂ were 81–17 min at ZVI concentrations of 0.15–2.5 g/L, respectively. X-ray absorption spectroscopy (XAS) confirmed that almost all As(III) was converted to As(V) after 2 h of reaction in the pH range 5–9. Addition of 9.6 μM H₂O₂ to 0.15 g/L ZVI suspensions diminished half-lifes for arsenic removal from 81 to 32 min and for As(III) oxidation from 77 to 8 min, i.e., by approximately a factor of 10. The increased rate of As(III) oxidation is attributable to enhanced formation of oxidants by the Fenton reaction with higher initial concentrations of H₂O₂. In practice, results of this study suggest that addition of small amounts (<1 mg/L) of H₂O₂ in various forms (e.g. stable and widely available Na-percarbonate) to water prior to treatment could significantly enhance As(III) oxidation and removal with ZVI.