74(Bi1/2Na1/2)TiO{i3}-20.8(Bi1/2K　1/2)TiO3-5.2BaTiO3-x　MnCO3　lead-free　piezoelectric　ceramics　were　synthesized　by　conventional　solid　oxide　routine.　The　tetragonal　74(Bi1/2Na1/2)TiO3-20.8(Bi　1/2K1/2)TiO3-5.2　BaTiO3　(BNKB)　exhibits　high　depolarization　temperature　Td　of　195C;　however,　its　properties　are　far　from　satisfactory　for　practical　application　and　need　to　be　improved.　The　experiments　show　that　the　addition　of　MnCO3　reduces　the　tetragonality　c/a　and　increases　the　cell　volume.　In　addition,　it　revealed　that　the　suitable　addition　of　MnCO3　promotes　the　sintering　and　increases　the　densities　of　BNKB　ceramics.　The　addition　of　MnCO3　also　enhances　the　relaxor　behavior　of　BNKB　ceramics　due　to　the　reconstruct　of　the　disorder　arrays.　Due　to　the　effect　of　the　crystal　lattice,　grain　growth,　and　relaxor　behavior,　the　optimal　electric　properties　were　realized　at　MnCO3　addition　x　of　0.16:　the　dielectric　permittivity　r　=　1047,　dielectric　dissipation　tan　=　0.022,　piezoelectric　strain　d33　=　140　pC/N,　mechanical　coupling　kp　=　0.18,　mechanical　quality　Qm　=　89　while　the　depolarization　temperature　Td　stays　relatively　high　at　175C.　The　effect　and　mechanism　of　Mn　doping　on　the　electrical　properties　were　discussed　in　detail.　©　2006　IEEE.