The oxidation of antimony (Ⅲ) in soils was studied using X-ray absorption fine structure (XAFS) spectra.An andosol soil sample and artificial soil samples (SiO2 blended with iron (Ⅲ) hydroxide and manganese (Ⅳ) oxide) were used herein.After adding antimony (Ⅲ) oxide to all soil samples,the oxidation process was observed by recording the XAFS spectra of Sb K-edge,Fe Kedge,and Mn K-edge.The results indicated that manganese (Ⅳ) oxide played an important role in the oxidation of Sb(Ⅲ);however iron (Ⅲ) hydroxide was not directly related to the reaction.During a 2-hr continuous Sb K-edge X-ray absorption near edge structure (XANES) measurement with an interval of 1 min of one of the artificial soil samples (SiO2 + MnO2 + Sb2O3),a pseudo-first-order reaction was determined with an average estimated rate of 0.52 ± 0.04 hr-1.Compared to the lower oxidation rate of andosol,it is suggested that because of the low concentration of Mn(Ⅳ) in natural soils,the oxidation process of Sb(Ⅲ) might be relatively slow and require more time to convert Sb(Ⅲ) to Sb(Ⅴ).