A new rock-salt type compound, namely Li3MgNbO5, was synthesized using traditional two-step sintering process for the first time. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermal dilatometer and network analyzer. The Li(3)MgNbO(5)ceramic sintered at 1260 degrees C adopted a cubic structure with Fm-3 m space group and exhibited excellent microwave dielectric properties (MDPs) of epsilon(r) = 16.2, Q x f = 96796 GHz, and TCF = - 24.8 ppm/degrees C. The fitting results of the infrared spectrum indicated that the dielectric polarization of Li3MgNbO5 in microwave frequency band was contributed by phonon absorption in infrared band. Furthermore, the negative TCF value of Li3MgNbO5 ceramic was compensated with a traditional TCF compensator similar to CaTiO3. A near-zero TCF value of + 1.2 ppm/degrees C was achieved in the composite 0.96Li(3)MgNbO(5)-0.04CaTiO(3) ceramics with epsilon(r) = 18.4 and high Q x f = 86625 GHz, exhibiting a great potential to be applied in microelectronics systems.