Ferrous sulfide (FeS) is an important carrier for metal(loid)s in anoxic environments, but the effect of FeS on the behavior of Sb is poorly understood. This work investigated the interaction of Sb(III) with FeS under anoxic condition. FeS was synthesized and both equilibrium and kinetic experiments on the interaction of Sb(III) with synthesized FeS were conducted at various pH values. The final solid phases were examined by SEM, XRD, TEM, and XPS. The results showed that the uptake of Sb(III) by FeS increased as pH decreased. The kinetic experiment at pH 5 obviously showed that the temporal decrease of Sb(III)aq coincide with the partial dissolution of FeS. In contrast, both the concentrations of Sb(III)aq and FeS in the kinetic experiment at pH 9 did not vary with time. The examination of the solid phases revealed the formation of amorphous Sb2S3 in the experiments at pH 5 and 7.5. Different mechanisms were suggested to affect the interaction of Sb(III) with FeS under acidic and alkaline conditions. At pH 9, adsorption dominated in the interaction. The decrease of Sb(III)aq and the concomitant partial dissolution of FeS at pH 5 indicated the replacement of FeS by Sb2S3, which was more significant at lower pH. The replacement of FeS by Sb2S3 was a relatively slow process compared to the acidic dissolution of FeS. The result of this study helps understand the mobility of Sb in anoxic environments and may favor the remediation of Sb contamination by the use of FeS.