We　prepared　bulk　nanocrystalline　SmCo6.6Nb0.4　sintered　magnet　material　by　spark　plasma　sintering　technique.　X-ray　diffraction　patterns　show　that　the　magnet　exhibits　a　stable　TbCu7　structure.　Transmission　electron　microscopy　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　under　a　7　T　magnetic　field,　the　coercivity　of　the　magnet　reaches　as　high　as　2.8　T;　the　saturation　magnetization　and　the　remanence　are　69.6　and　51.4　emu/g,　respectively.　The　magnet　exhibits　good　thermal　stability　with　the　coercivity　of　0.48　T　at　773　K,　and　the　coercivity　temperature　coefficient　beta　of　-0.169%/K.