Samples　of　20wt.%Ti-6Al-4V　particles　reinforced　MB15　magnesium　matrix　composite　were　fabricated　by　powder　metallurgy　route.　Densities　of　sintered　and　extruded　samples　were　measured　using　Archimedes＇　principle.　Deformation　and　micro　structure　of　extruded　bars　were　investigated　with　optical　microscope　and　scan　electric　microscope　(SEM).　Effects　of　hot-extrusion　on　micro　structure　and　mechanical　properties　were　studied　by　microstructure　observation　and　tensile　tests.　The　results　show　that　the　lower　density　of　sintered　sample　is　increased　by　hot-extrusion　approximately　near　theoretical　density　of　the　composite;　and　both　of　deformation　and　microstructure　were　uneven　in　the　outer　layer　and　the　center　of　hot-extruded　bars;　moreover,　the　second　extrusion　could　further　decrease　the　matrix　grain　size　and　increase　the　mechanical　properties　when　compared　with　the　first　extrusion.　Therefore,　Ti-6Al-4V　particles　can　be　used　to　strengthen　Mg　and　Mg　alloys,　and　its　reinforcing　effect　may　be　more　superior　to　that　of　SiC　particles.