Herein,　to　enhance　the　long-term　stability,　ZnO　varistor　ceramics　mixed　with　Bi2O3,　Sb2O3,　MnCO3,　Co2O3,　SiO2,　and　different　concentrations　of　NiO　(with　0,　0.3,　0.7,　1,　1.3,　1.6　mol%)　were　grown　for　controlling　the　Bi2O3　intergranular　phase　as　α-Bi2O3　using　a　well-known　ceramic　process　technology.　The　microstructure　and　crystalline　phases　were　investigated　using　scanning　electron　microscopy　(SEM),　X-ray　energy　dispersive　spectrometry　(EDS),　X-ray　diffraction　(XRD),　and　transmission　electron　microscopy　(TEM).　The　electrical　properties　were　evaluated　using　a　high-voltage　DC　power　supply,　current　pulse　generator,　oscilloscope,　and　impedance　analyzer.　Results　from　XRD　patterns　and　TEM　indicated　that　the　NiO　dopant　enables　the　transition　of　δ-　to　α-Bi2O3　phase.　Current　density-electric　field　measurements　revealed　that　NiO-doped　ZnO　ceramics　have　an　increased　breakdown　field　and　decreased　leakage　current　density.　During　DC　aging,　the　power　loss-aging　time　curves　of　NiO-doped　ZnO　ceramics　with　increased　α-Bi2O3　phase　showed　a　downward　trend,　indicating　increased　stability.　The　current　research　has　revealed　that　improving　the　electrical　stability　of　polycrystalline　ceramics　via　intergranular　phase　control　might　be　feasible　for　the　emerging　DC　power-based　aging　applications.　©　2021　Elsevier　B.V.