Abstract: The poisoning effects of alkali metals on low-temperature selective catalytic reduction (SCR) catalyst MnO_x-CeO₂/ZrO₂-PILC were invested by the method of impregnation in the laboratory. It was indicated that the addition of Ca/Mg would decrease the activities of the catalyst, and the poisoning effects were contacted with the amount and acidity of the doped-alkali metal. X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), N₂ adsorption-desorption and temperature-programmed desorption of NH₃ (NH₃-TPD) were used to characterize the properties of the fresh and alkali earth doped catalysts. According to the results, the doped-alkali metals would inhibit the reduction properties, induce the loss in surface area and surface acidity.