Relaxor　ferroelectric　Pb(Sc1/2Nb1/2)O-3　(PSN)　superfine　ceramics　were　fabricated　by　spark　plasma　sintering　process　and　subjected　to　an　annealing　in　oxygen　ambience　at　a　low　temperature　of　500　degrees　C.　The　microstructure　of　the　PSN　ceramics　was　examined　by　X-ray　diffraction　and　scanning　and　transmission　electron　microscopy,　while　the　dielectric　properties　were　measured　in　the　range　of　25-200　degrees　C.　The　dielectric　measurements　revealed　a　reverse　change　in　the　frequency　dispersion　Delta　T　and　diffusive　factor　lambda　as　annealing　extended.　Transmission　electron　microscopy　observation　and　conductivity　measurement　revealed　that　the　uncommon　performance　in　relaxor　properties　could　be　attributed　to　the　complex　effects　of　oxygen　vacancies　and　domain　structures　induced　by　the　annealing.