Transformation and transport of Sb are significantly influenced by oxidation in natural environment, therefore, as an effective oxidant for Sb(III), MnO₂ may have essential impacts on the ecological effects of Sb in waters contaminated by acidic mine drainage or wastewater containing high concentrated Sb. The present research investigated the effects of coexisted Fe(II) on oxidation and adsorption of Sb(III) by MnO₂ under acidic conditions. Results of kinetic experiments showed that oxidation and adsorption of Sb(III) by MnO₂ were both influenced by Fe(II) in Sb(III)-Fe(II) simultaneous oxidation system and Fe(II) pretreated system. Oxidation was inhibited yet adsorption was promoted in the presence of soluble Fe(II), and both effects were enhanced with increasing ratio of Fe(II): Sb(III). Through scanning electron microscope, energy dispersive spectrometer, X-ray diffraction and X-ray photoelectron spectroscopy analysis, it was confirmed that Fe(III) compounds were formed around MnO₂ particles, and they were the reason that caused inhibition of Sb(III) oxidation. However, two different Fe(III) compounds were formed around MnO₂ particles when Fe(II) intervened experiment systems in different ways. In simultaneous oxidation system, poorly crystallized or amorphous Fe-Sb precipitates (probably FeSbO₄) were formed around MnO₂ particles after competitive oxidation of Sb(III) and Fe(II), while in Fe(II) pretreated oxidation system, Fe(II) pretreatment caused formation of schwertmannite around MnO₂ particles. Both Fe(III) compounds prevented the direct contact of Sb(III) with MnO₂ surface, but most Sb(III) could still diffuse through both Fe(III) compounds and be oxidized by MnO₂, while part of the Sb(III) was adsorbed by Fe(III) compounds. The newly formed Sb(V) was firstly adsorbed by Fe(III) compounds, and then released into solution after reaching adsorption saturation. The present study revealed that Fe(II) was critical to Sb(III) oxidation and adsorption by MnO₂, and the influence mechanisms were different when Fe(II) intervened the reaction systems through different ways.