With a purpose of obtaining materials showing high specific strength at room temperature combined with superplastic elongation at elevated temperatures, Mg-8Ag (mass%) alloys with various ternary alloying additions were rapidly solidified by gas atomizing and subsequent splat quenching. Ternary alloying elements studied were Cu, Al, Zn, Ca and Ce. The rapidly solidified flakes were consolidated to the P/M materials by hot extrusion at 573K. The structures and mechanical properties were studied on the as-extruded P/M materials before and after heating at various temperatures. The highest tensile strength of 580 MPa was obtained at room temperature for Mg-8Ag-8Ce alloy with elongation higher than 3%. This corresponds to a high specific strength of 290 MPa/Mg/m(3). At 473K, the highest tensile strength of 334 MPa was observed for Mg-8Ag-5Ca alloy. Tensile elongation increased with rising test temperature and superplastic elongation of above 200% was observed at 573K for Mg-8Ag-8Al, Mg-8Ag-8Zn and Mg-Mg-5Ca alloys. The largest elongation of above 300% was observed for the as-extruded P/M materials of Mg-8Ag-8Al and Mg-8Ag-5Ca alloys at an initial strain rate of 1.7x10(-2)/s.