The　single-phase　Sm2Co17　alloys　with　amorphous　and　nanocrystalline　structures　were　prepared　separately　by　a　simplified　route　combining　high-energy　ball　milling　and　spark　plasma　sintering.　The　microstructure　evolution,　as　well　as　the　phase　transformation,　were　investigated　for　the　prepared　Sm2Co17　alloys.　It　was　found　that　the　nanocrystalline　Sm2Co17　alloy　has　a　stable　hexagonal　crystal　structure　at　the　room　temperature,　which　shows　different　phase　stability　from　the　conventional　polycrystalline　Sm2Co17　alloys.　In　contrast　with　the　coarse-grained　Sm2Co17　ingot　that　shows　very　weak　permanent　magnetic　properties,　the　amorphous　and　nanocrystalline　Sm2Co17　alloys　exhibit　apparently　improved　magnetic　properties.　The　first-principles　calculations　show　that　a　much　higher　spin　polarization　is　achieved　in　the　nanocrystalline　Sm2Co17,　as　compared　with　the　coarse-grained　polycrystalline　counterpart.　Due　to　the　intense　spin　polarization　at　the　Fermi　level,　the　exchange　interaction　between　Sm　(4f)　and　Co(3d)　electrons　is　enhanced,　which　results　in　the　strong　magnetism　in　the　nanocrystalline　Sm2Co17　alloy.　(C)　2010　Elsevier　Ltd.　All　rights　reserved.