BaTiO3-based dielectric ceramics with grain sizes of 100-120 nm were prepared by the chemical coating approach and are promising for the application of ultrathin multilayer ceramic capacitors. The doping effects of Mg on the microstructures and dielectric properties of the BaTiO3-based ceramics were investigated. The addition of Mg was beneficial for inhibiting the grain growth and improving sintering characteristics and improving the dielectric properties and reliability of the nano-BaTiO3-based ceramics. The highly accelerated lifetime test and thermally stimulated depolarization current were employed to study the resistance degradation and conduction mechanism of the Mg-doped BaTiO3 ceramics. It was determined that the reliability characteristics greatly depended on the Mg content. The addition of 2 mol% Mg was suitable for improving the reliability of the nano-BaTiO3-based ceramics, which is an important parameter for the application of multilayer ceramic capacitors. However, further increasing the addition amount of Mg decreased the performance of the BaTiO3-based ceramics.