[en] The effects of B₂O₃ additives on the microstructures and the microwave dielectric properties of complex perovskite 0.66Ca(Mg_1/3Nb_2/3)O₃-0.34CaTiO₃ ceramics were investigated. The B₂O₃ additives, acting as a sintering aid, can effectively lower the sintering temperature of the ceramics to as low as 1200 deg. C. No second phase was observed throughout the entire experiments. Moreover, boron was not found in the grains but residual at the boundaries indicating a liquid phase sintering. At 1250 deg. C, the 0.25 wt% B₂O₃-doped 0.66Ca(Mg_1/3Nb_2/3)O₃-0.34CaTiO₃ ceramics possesses a relative permittivity ε_r of 43.94, a Q x f value of 30,000 GHz (measured at 6.7 GHz) and a τ_f value of -1.9 ppm/deg. C. It exhibits a substantial temperature reduction (>200 deg. C) and compatible dielectric properties in comparison with that of un-doped one