30-nm-grain-sized　potassium　sodium　niobate　((K0.5Na0.5)NbO3　(KNN))　powders　were　obtained　with　the　sol-gel　method.　From　these　powders　as　starting　materials,　high-density　KNN　ceramics　with　a　relative　density　of　98.9　%　and　grain　size　of　500　nm　were　prepared　with　the　spark　plasma　sintering　(SPS)　method.　The　processing　parameters　were　a　sintering　temperature　of　900　degrees　C,　sintering　pressure　of　30　MPa　and　sintering　time　of　3　min.　The　phase　composition,　microstructure　and　electrical　properties　of　the　ceramics　have　been　investigated.　The　results　show　that,　unlike　common　micro-grained　ceramics,　submicron-grained　ceramics　prepared　with　the　SPS　method　show　obvious　dielectric　relaxation　(dispersion　factory　is　1.31).　Meanwhile,　the　KNN　ceramics　exhibit　good　electrical　properties　such　as　dielectric　constant　epsilon(r)　=　753,　piezoelectric　constant　d(33)　=　142　pC/N　and　electromechanical　coupling　factor　k(p)=　0.41.