High　permittivity　and　low　dielectric　loss　are　important　for　the　application　of　high-temperature　dielectrics.　In　present　study,　high　temperature　dielectrics　based　on　(1-x)　[(Na0.5Bi0.5)0.92Ba0.08]0.955La0.03TiO3-xNaNbO3　compositions　were　synthesized　by　a　conventional　solid-state　reaction　method.　The　microstructure,　dielectric,　ferroelectric　and　electrical　properties　were　systematically　investigated.　All　the　samples　show　relatively　high　permittivity　and　excellent　low　dielectric　loss　range　from　∼90　°C　up　to　400　°C.　Impressively,　the　composition　x　=　0.06　shows　a　high　permittivity　of　2436　at　150　°C　(1　kHz),　(Εr−Εr150°C)/Εr150°C　varying　no　more　than　15%　in　the　temperature　range　of　54　°C–344　°C　together　with　a　low　loss　(tanδ≤0.02)　range　between　92　°C　and　400　°C.　By　developing　highly-localized　complex　defect-dipoles　with　La　and　NaNbO3　dopants　to　restrain　the　mobility　of　oxygen　vacancy,　as　verified　by　XPS　and　resistivity-temperature　results,　the　dielectric　loss　is　limited　to　rather　low　values.　Hence,　the　current　system　will　be　a　promising　candidate　in　high　temperature　ceramic　capacitors.　©　2020　Elsevier　B.V.