In　this　work,　perovskite　Na　0.5　Bi　0.5　TiO　3　is　applied　as　oxygen-defect　conductor　of　NO　2　sensor　fabricated　with　CuO　as　the　sensing　electrode　and　Pt　as　reference　electrode.　Transition　metal　ion　Cu　2+　serves　as　a　dopant　of　Na　0.5　Bi　0.5　TiO　3　at　B　site　in　view　of　its　dual　functions　in　both　creating　as　many　oxygen　vacancies　as　possible　and　extending　the　length　of　the　triple　phase　boundaries　together　with　CuO　sensing　electrode.　The　phase　transformation　from　the　cubic　to　rhombohedral　phase　occurs　in　the　process　of　increasing　Cu　2+　contents,　resulting　in　greater　lattice　distortion　and　thus　generating　more　oxygen　vacancies.　The　expansion　of　the　lattice　volume　and　the　overflowed　Bi　2　O　3　promote　oxygen　hopping　in　the　[BO　6　]　∝　chains　of　the　solid　electrolyte.　The　electrochemical　results　indicate　that　the　Na　0.5　Bi　0.5　Ti　0.85　Cu　0.15　O　3-δ　sensor　exhibits　excellent　response-recovery　characteristics　with　high　sensitivity　(24.49　nA/ppm)　upon　exposed　to　500　ppm　NO　2　at　500　°C.　The　possible　coexistent　gases　affect　little　on　the　response　current　of　the　sensor　towards　NO　2　gas.　The　long-term　stability　measurement　illustrates　that　there　is　only　a　slight　1.36　μA　drop　in　response　current　value　after　aging　storage　for　one　and　a　half　months.　The　performances　of　the　sensors　based　on　non-rare-earth　Cu-doped　Na　0.5　Bi　0.5　TiO　3　solid　electrolytes　exhibit　the　better-off　application　prospect　with　low　cost　at　low-medium　temperature.　©　2019　Elsevier　Ltd　and　Techna　Group　S.r.l.