MnO2 and Nb2O5 co-doped 0.9BaTiO(3)-0.1(Bi0.5Na0.5)TiO3 powders with excellent dielectric properties were fabricated using a conventional solid-state reaction method and sand milling. The doping effects of various amounts of MnO2 on the dielectric properties were investigated. The results revealed that the dielectric properties greatly depended on the concentration of MnO2. All the ceramics met the X9R specification. The dielectric loss decreased with an increasing concentration of MnO2. The specimen with an appropriate amount of 0.2 mol% MnO2 exhibited the most enhanced properties: high insulation resistance (2.49 x 10(13) omega/cm) and improved degradation properties. Multilayer ceramic capacitor (MLCC) chips were prepared by tape casting using a 0.2 mol% Mn-doped 9010BTBNT-based ceramic powder. The capacitance of the MLCC chip was approximately 100 nF, and the dielectric loss was approximately 1.75% at room temperature. The high-temperature accelerated lifetime was over 1000 hours under 250 V (five times the working voltage) and at 230 degrees C, indicating that the MLCC chips possess superior reliability.