(1-x)(K0.495Na0.495La0.01)(Nb0.997Cu0.0075)O-3-xBi(Mg0.5Zr0.5)O-3 (abbreviated as KNLNC-xBMZ) ceramics were designed and prepared. The phase transition, microstructure and electrical properties of the ceramics were investigated. The phase structures of the ceramics transform from orthorhombic to pseudocubic phases and the grain sizes decrease gradually with BMZ content (x) increasing. Additionally, BMZ additions can significantly enhance the dielectric temperature stability and decrease the dielectric loss of ceramics over a relatively broad temperature range. KNLNC-0.02BMZ ceramics exhibit high dielectric permittivity (epsilon(r) = 1542) and small variation (Delta epsilon(r)/epsilon(r150 degrees C) <= +/- 15%) in dielectric permittivity from 100 to 375 degrees C, and low dielectric loss (tan delta <= 2%) in the temperature range of 100-350 degrees C, which suggests that this ceramic is a candidate for high-temperature capacitor application.