High　temperature　superconductor　YBa2Cu3O　7-x　(YBCO)　nanopowders　were　successfully　prepared　by　a　citrate　pyrolysis　technique.　The　phase　formation　and　microstructure　of　the　nanopowders　were　studied.　The　microstructure　analysis　shows　that　the　obtained　YBCO　powders　have　very　fine　grains　with　a　size　around　several　tens　of　nanometers.　The　superfine　morphology　reveals　that　the　thermal　agglomeration　of　the　particles　decreases　with　decreasing　the　annealing　temperature　and　shortening　the　annealing　time.　In　addition,　the　complete　phase　formation　of　YBCO　depends　upon　the　annealing　temperature　and　the　annealing　time　as　well.　So　far,　these　nanopowders　have　been　used　to　fabricate　the　melt-textured　YBCO　bulk　materials.