Lead-free　piezoelectric　ceramics　Sr2-xCaxNaNb5O15+ywt%　MnO2　(x=0.05-0.35,　y=0,　0.3,　0.5)　(SCNN-M)　were　fabricated　by　conventional　solid-state　processes,　and　their　microstructure,　phase　transformation,　dielectric,　piezoelectric　and　ferroelectric　properties　were　investigated　systematically.　Our　results　reveal　that　Ca2+　ions　have　entered　into　the　Sr2NaNb5O15　lattices　to　form　a　solid　solution　and　the　doping　of　MnO2　is　effective　in　promoting　the　densification　of　the　ceramics.　With　the　MnO2　doping,　all　the　ceramics　can　be　well　sintered　at　a　relative　low　temperature　and　exhibit　a　dense　and　pure　tungsten-bronze　structure.　The　addition　of　Ca2+　has　no　remarkable　effect　on　the　microstructure　and　MnO2　caused　a　significant　promoted　grain　growth.　Compared　with　the　pure　SCNN　ceramics,　the　dielectric　and　piezoelectric　properties　of　SCNN-M　ceramics　were　greatly　enhanced.　At　room　temperature,　the　SCNN-M　ceramics　with　x=0.5　and　y=0.5　exhibits　the　optimum　properties:　piezoelectric　coefficient　d(33)=190pC/N,　mechanical　quality　factor　Q(m)=1455,　planer　electromechanical　coupling　factors　K-p=13.4%,　thickness　electromechanical　coupling　factors　K-t=36.5%,　dielectric　constant　epsilon(r)　=2123,　loss　tangent　tan　delta=0.038,　remanent　polarization　P-r=4.76　mu　C/cm(2),　spontaneous　polarization　P-s=9.36　mu　C/cm(2),　coercive　field　E-c=12.68kV/cm,　and　curie　temperature　T-c=260　degrees　C.　Therefore,　the　SCNN-M　ceramics　are　a　good　candidate　material　for　lead-free　piezoelectric　ceramics.