Effects　of　Sn　on　microstructure　and　mechanical　properties　of　AZ61　magnesium　alloy　have　been　investigated.　Microstructural　observation　indicates　that　the　spheroidal　Mg2Sn　particle　is　created　in　both　as-cast　and　heat　treated　AZ61　alloy　with　Sn　addition.　A　few　Sn　addition　can　increase　the　tensile　strength　and　yield　strength　of　the　alloy.　With　3%　Sn　addition,　the　tensile　strength　and　yield　strength　of　heat-treated　AZ61　alloy　can　reach　274　MPa　and　172　MPa,　respectively,　while　elongation　is　decreased　to　9%.　With　Sn　addition,　fracture　morphology　is　transformed　from　cleavage　rupture　into　quasi-cleavage　rupture　from　SEM　observation.