Fine-grain BaTiO3-based ceramics co-doped with different amounts of Ho and Dy were prepared by a chemical coating method, giving good dielectric properties and gentle temperature stability. The co-doping effect on the dielectric properties and microstructure evolution of BaTiO3-based ceramics was investigated. The highly accelerated lifetime test was conducted to study the failure of the insulation resistance under high electric field and elevated temperature. Results showed that ceramic samples with Ho and Dy co-doping exhibit better insulation degradation behavior than those with Ho or Dy doped separately. Impedance analysis proved that different co-doped amounts of Ho and Dy show almost no effect on the resistance and the activation energy of grain boundary in BaTiO3-based ceramics. However, there was an obvious difference on the resistance and the activation energy for grain bulk. The synergistic effect of Dy and Ho is helpful to improve the reliability of BaTiO3-based multilayer ceramic capacitors. (C) 2015 Published by Elsevier Ltd.