Rare　earth　(RE)　nanoparticles　with　single-crystal　structure　and　controllable　size,　and　RE　nanocrystalline　bulks　with　ultrafine　grain　sizes　(3-8　nm),　were　prepared　with　a　home-configured　＇oxygen-free＇　in　situ　synthesis　system.　Systematic　investigations　revealed　the　characteristic　structures　and　properties　of　the　nano　REs.　As　compared　with　the　conventional　polycrystalline　REs,　the　prepared　ultrafine　nanocrystalline　REs　show　remarkably　different　physical,　thermal　and　mechanical　properties,　which　are　of　broad　scientific　and　engineering　interest.　The　series　of　structure　and　property　characterizations　are　significant　to　further　develop　the　fundamental　database　for　the　nano　REs.　As　a　particular　contribution　to　the　characterization　of　the　RE　family　on　the　nanoscale,　this　work　implements　a　clear　guideline　for　the　composition　design　and　the　scale　control　in　the　development　of　advanced　nano　RE　functional　and　structural　materials.　©　IOP　Publishing　Ltd　and　Deutsche　Physikalische　Gesellschaft.