The　single-phase　ultrafine　nanocrystalline　SmCo3　compound　with　a　high　coercivity　of　33　kOe　and　a　Curie　temperature　of　925　K　was　prepared　using　a　simple　and　efficient　method,　which　took　advantages　of　the　concurrent　processes　of　nanocrystallization　and　densification　during　spark　plasma　sintering.　The　crystal　structure　of　the　nanocrystalline　SmCo3　compound　was　constructed.　As　compared　with　the　conventional　microcrystalline　SmCo3　compound,　a　large　axial　ratio　c/a　=　4.920　and　an　expansion　of　the　unit　cell　volume　of　2.97%　were　obtained　in　the　lattice　structure　of　the　nanocrystalline　SmCo3.　The　relationship　between　the　magnetic　properties　and　the　nanocrystalline　structure　was　analyzed.　A　specific　magnetic　transition　from　the　weak　ferromagnetic　to　the　strong　ferromagnetic　state　was　discovered　in　the　nanocrystalline　SmCo3　compound,　which　was　considered　to　be　related　to　the　large　anisotropic　strain　in　the　crystal　lattice.