$0.7Ba(Mg{frac}_{1}{3}Ta{frac}_{1}{3})O_3-0.3Ba({frac}_{1}{3}Nb{frac}_{1}{3})O_3ceramics$ were prepared by the conventional mixed oxide method. The ceramics were sintered at the temperature of $1500{sim}1575[^{circ}C]$ for 5 hours in air. The microwave dielectric properties of the specimens were investigated with sintering temperature. The 0.7BMT-0.3BCN ceramics showed typical XRD patterns of the complex perovskite structure. Dielectric constant and quality factor were increased with increasing the sintering temperature. In the case of the specimens sintered at $1575[^{circ}C]$ for 5 hours, dielectric constant, quality factor and temperature coefficient of resonant frequency were good values of 28,23545 at 10[㎓] and -1.2 $[ppm/^{circ}C]$, respectively.