Failure mechanism of a multilayer ceramic capacitor (MLCC) made of a low-fire BaNd(2)Ti(4)O(12)(BNT)+ZnO-B(2)O(3) (ZB) dielectric with an inner pure silver electrode at elevated temperatures and voltages has been investigated. A nonlinear current-voltage leakage characteristic is found when the degradation of MLCC occurs, and the time to failure decreases with increasing either the temperature or the voltage. Results of microstructure, composition, and impedance analyses reveal that the failure is caused by silver diffusion in the ZB glass during sintering and highly accelerated life test.