Low-temperature sintered 0.99((1-x)Bi0.5Na0.5TiO3-xNaNbO3)-0.01Sr0.8Na0.4Nb2O6 (100xNN, x=0.25 and 0.30) ceramics and MLCC were successfully prepared, and the dielectric properties were systematically investigated. The dielectric permittivity at 25 °C (ε′25°C) of 25NN ceramic is 1088, and the dielectric variation is small between -88 °C and -400 °C (|△ε′/ε′25°C| ≤ 15%, △ε′=ε′-ε′25°C). The dielectric loss tangent (tanδ) of 25NN ceramic is less than 0.02 between -65 °C and 358 °C. The MLCC with 25NN ceramic dielectrics and Ag inner electrode also has excellent dielectric stability, of which |△ε′/ε′25°C| is less than 15 % between -100°C and 400°C, and the dielectric loss is less than 0.02 between -88°C and 373°C. All these results indicate that the low-temperature sintered MLCC with Ag inner electrodes is a promising capacitor in automobile engines and aerospace fields, where the usage temperature is often above 300 °C.