There is provided a process of preparing low-temperature sintered microwave dielectric ceramics, prepared by a process comprising co-precipitating Nb and Bi or Zn in an aqueous basic solution to obtain a BiNbO.sub.4 or Zn.sub.3Nb.sub.2O.sub.8 precursor powder, thermally decomposing the powder to obtain BiNbO.sub.4 or Zn.sub.3Nb.sub.2O.sub.8 powder, adding CuO and V.sub.2O.sub.5, pulverizing and sintering the mixture, which produces ceramics having small dielectric losses (Qf.sub.0>15,000 GHz) and high dielectric constant (k=20 45) at microwave frequencies by sintering at a low temperature of 700 to 750.degree. C. Thus, the microwave dielectric ceramics prepared in accordance with the present invention can be advantageously used in multi-layer ceramic packaging such as filter planar antenna, microwave oscillator, etc., which comprise base metals such as silver (Ag) and copper (Cu) as an internal electrode.