The grain size of Mg foams was innovatively refined without alteration of pore structure and relative density by subjecting multi-axial forging (MAF) process to Ti-Mg composite,an intermediary product of the fabrication process of Mg foams where the spherical Ti particles were utilized as the replication material.The feasibility of the MAF process and the grain size effect on the mechanical properties of Mg foams were discussed.The results showed that,with the appropriate strain of 0.24 applied in the MAF process,Ti-Mg composites returned to original physical appearance without generating micro-cracks.And complete recrystallization was achieved after heat treatment,with the grain size of the MAF-processed Mg foams two to three orders of magnitude smaller than that of as-cast foam.The mechanical properties of Mg foams were enhanced extensively after grain refinement with the yield strength and the plastic collapse strength increased by 147％ and 50.7％,respectively.A revised model integrated by the Hall-Petch law and Gibson-Ashby model was proposed,which gave a good estimation of the yield strength and the plastic collapse strength of Mg foams from the compressive behavior of the corresponding parent material,though a knockdown factor of 0.45 was introduced for the yield strength.