Determination of the oxidation state of Sb by X-ray absorption near-edge structure spectroscopy was conducted to soil samples in natural mine tailing and laboratory experiments. It was found that Sb was in oxidized form, Sb(V), rather than Sb(III) in soil under reductive condition in laboratory experiments (Eh = -222mV, pH 5.2) and in natural mine tailing samples (Eh = - 17 mV, pH 7.7). These results suggested that Sb exists dominantly as Sb(V) in soil under wide range of natural redox conditions.