Adopting　a　novel　synthesizing　method-low　temperature　reaction　melting　(LRM),　a　MgO　particulate　reinforced　magnesium　matrix　composite　was　in-situ　fabricated　using　pre-oxidized　Mg　powders.　The　microstructures　and　mechanical　properties　of　the　composite　were　investigated　by　microstructure　observation　and　tensile　tests.　The　results　showed　that,　due　to　the　melting　of　Mg　powders　during　LRM　treatment,　the　oxide　film　on　the　surface　of　Mg　powder　was　effectively　broken　into　pieces,　refined　and　subsequently,　spheroidized　into　particulates　with　micron　or　sub-micron　sizes　by　the　joint　effect　of　the　liquid　phase　Mg　and　the　surface　tension　of　MgO　itself.　Moreover,　The　formed　MgO　particulates　possess　not　only　good　interfacial　bonding　with　the　matrix　and　uniform　distribution,　but　also　high　strength　and　stiffness,　which　is　beneficial　to　improving　the　reinforcement　effect　to　the　matrix.　As　a　result,　the　LRM　method　can　bring　better　microstructures　and　mechanical　properties　to　the　composite　compared　to　powder　metallurgy　process.