Mg2Si/Mg-5Zn-2.　5Er　composites　were　fabricated　by　repeated　plastic　working　(RPW)　via　solid　state　reaction　and　hot　extrusion.　Number　of　RPW　was　100,　200,　300　and　400,　respectively.　Effects　of　RPW　times　on　microstructure　and　mechanical　properties　of　the　composites　were　investigated　by　XRD　(X-ray　diffraction),　SEM　(scanning　electron　microscope)　and　OM　(optical　microscope).　The　results　show　that　with　increasing　in　RPW　times,　size　of　Mg2Si　phase　is　gradually　decreased　with　more　uniform　distribution.　With　200　times　RPW,　the　composites　exhibit　desirable　comprehensive　mechanical　properties,　and　average　grain　size　in　the　composites　reaches　1.　8　μm,　decreased　by　81.　6%　compared　with　that　of　samples　without　RPW,　which　is　attributed　to　the　grain　refinement　caused　by　repeated　plastic　deformation　and　grain　growth　caused　by　dynamic　recrystallization　during　solid　state　reaction　and　hot　extrusion.　In　addition,　tensile　strength　reaches　394MPa,　increased　by　25.　4%　compared　with　that　of　ones　without　RPW,　and　elongation　makes　5.　5%.　The　strengthening　mechanism　of　the　prepared　composites　is　characterized　by　grain　refinement.