Antimonite (Sb(III)) contamination has raised global concern due to its high toxicity. This study investigated the oxidation and sequestration of Sb(III) from solution onto newly formed biogenic Mn oxides (BMO), using batch experiments and spectroscopic analyses. Kinetic experiments indicated that Sb(III) was quickly oxidized and sequestrated after 10 min by BMO at a pH of 7.0. Bacterial activity in BMO did not significantly affect Sb(III) sequestration. X-ray photoelectron spectrometer (XPS) analysis indicated that Sb(V) was the only species remaining in the solid phase after the reaction of Sb(III) with BMO. Chemical extraction experiments with the (NH₄)₂HPO₄ and NH₂OH·HCl showed that the dominant fractions of Sb(III) after the reaction included a Mn oxides bound fraction and residual fraction. XRD results further indicated that the rapid oxidation of Sb(III) by BMO contributed to the production of Mn(II) antimonate precipitates. The formation of less reactive Mn(III) blocked Sb(V) adsorption on the BMO surface. These results provide important experimental evidence related to the effect of BMO on the environmental behavior of Sb(III). The study concludes that BMO plays a key role in sequestration of environmental Sb(III).