The effects of Cerium (Ce) addition on microstructures and mechanical properties of hot-extruded AZ61 alloy were investigated. It is found that Ce refines Mg17Al12 particles and brings about precipitation of a new rod-like phase that is identified as Al4Ce by X-ray diffraction. During hot deformation, Al4Ce particles can refine dynamic recrystallized grains by impeding grain growth. For Ce additions up to 1.0 wt%, the recrystallized grain size decreases; When Ce addition is more than 1.0 wt%, grain size increases inversely. Strength and elongation of extruded or annealed specimens at room temperature increase along with Ce addition up to 1.0 wt%, then decrease. Optimal mechanical properties are correspondent to 1.0 wt% Ce addition. (C) 2004 Kluwer Academic Publishers.