This study investigates the influence of GeO 2 on the nonlinear coefficient (¡) and breakdown voltage (E B ) of TiO 2 Ta 2 O 5 CaCO 3 varistor ceramics doped with GeO 2 and prepared according to a conventional ball milling moldingsintering process. The electrical performance parameters, including the nonlinear coefficient (¡), breakdown electric field (E B ), and leakage current (J L ), were assessed using a varistor direct-current instrument. The average barrier height ) B of each sample was calculated using the relevant formula. Analyses conducted by X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy demonstrated that GeO 2 doping changed the microstructures of TiO 2 Ta 2 O 5 CaCO 3 ceramics, resulting increased ¡ and decreased E B values. Ceramics doped with 0.2 mol % Ta 2 O 5 , 0.2 mol % CaCO 3 and 0.9 mol % GeO 2 exhibited the maximum ¡ value (¡ = 9.8) and the highest grain boundary barrier () B = 0.92 eV) but a low E B value (E B = 17.2 V•mm ¹1 ).