MgO-Al2O3 mixed oxides were prepared and used as the support of Co-Mo-based water-gas shift reaction (WGSR) catalysts. X-ray diffraction (XRD) characterization showed that the MgO-Al2O3 mixed oxides support is composed of MgO, gamma-Al2O3, and magnesia-alumina spinel. The MgO-Al2O3 mixed oxides-supported Co-Mo-based catalysts exhibited high shift activity at high temperature (360-450 degrees C) and high stability. The addition of potassium enhanced the activities but affected adversely the stabilities of Co-Mo-based catalysts. ESR characterization shows that the Mo5+ species are not connected with the WGSR activity. Magnesium in the support may be closely related with the formation of formate species intermediate for the WGSR.