Bulk　nanocrystalline　SmCo6.6Nb0.4　sintered　magnet　was　prepared　by　spark　plasma　sintering　technique　(SPS).　Structure　and　magnetic　properties　of　magnet　was　studied.　XRD　patterns　show　that　the　magnet　exhibits　TbCu7　structure,　indicating　a　stable　1:7　phase　was　obtained　after　SPS　process.　TEM　observation　indicates　that　the　microstructure　of　the　magnet　is　composed　of　SmCo6.6Nb0.4　single-phase　grains　with　an　average　grain　size　of　30　nm.　Magnetic　measurement　shows　that　the　coercivity　of　the　magnet　reaches　as　high　as　2.8　T;　the　high　ratio　Mr/Ms　of　0.74　demonstrates　the　existence　of　strong　intergrairn　exchange　coupling　among　the　nanograms.　The　magnet　exhibits　a　good　thermal　stability　with　the　coercivity　of　0.48　T　at　773　K,　and　the　coercivity　temperature　coefficient　β　of　-0.169%/K.