Fe-Mn oxides was prepared by thermal activation of Mn-rich limonite at different temperatures, and then developed as catalysts for low-temperature NH3-SCR. The obtained samples were characterized by XRD, XRF, TEM, XPS, BET, H-2-TPR, NH3-TPD, NH3-SCR model reaction and in situ DRIFTS. The results indicated that Fe-Mn oxides catalyst derived from the thermal treatment at 300 degrees C (H300) exhibited an excellent NO conversion which was higher than 90% at a temperature range from 130 to 300 degrees C. The large surface area (95.9 m(2)/g), large amount of acid sites, suitable reduction behavior, and abundant surface hydroxyl positively responsed to the excellent performance of H300 for NH3-SCR. The results of in situ DRIFTS and kinetic study demonstrated that when the SCR reaction temperature reached to 100 degrees C, both the Eley-Rideal mechanism and the Langmuir-Hinshelwood mechanism might happen over H300. However, the Langmuir-Hinshelwood mechanism could be approximately neglected at higher reaction temperatures. This study favors the understanding of NH3-SCR mechanism of the prepared provides Fe-Mn oxides and explores new application field for Mn-rich limonite in low-temperature NH3-SCR.