The oxidative dehydrogenation of propane (ODHP) over NiO-Bi2O3-ZrO2 catalyst was carried out with a fixed-bed flow reactor at 400 degrees C under atmospheric pressure. NiO-Bi2O3-ZrO2 prepared by the co-precipitation method afforded moderate propane conversion of 18.6% and propylene selectivity of 56.1% at 400 degrees C. From XPS analyses of the used catalysts, NiO/ZrO2 prepared by the impregnation method exhibited reduced metallic Ni species after the ODHP for 1 h. On the other hand, NiO-ZrO2 and NiO-Bi2O3-ZrO2 prepared by the co-precipitation method exhibited predominantly NiO and Ni2O3 together with a minor amount of metallic Ni. From TPR and TPO, it was suggested that propylene was formed by the reaction with adsorbed oxygen species on NiOx, in contrast, metallic Ni promoted complete oxidation of propane to decrease propylene selectivity. Thus, to maintain Ni species in the oxidized state was crucial for the high selectivity to propylene. The additive effect of Bi2O3 is ascribed to have kept NiO in the solid solution less reducible state. In addition, once metallic Ni was formed, it could easily be oxidized to NiO or Ni2O3.