By a reaction-sintering approach Li3Mg2SbO5F2 oxyfluorides ceramics were prepared. The sinterability, microstructure,phase transition along with microwave dielectric performances of present ceramics were researched. A gradual phase transitionfrom cubic to orthorhombic in Li3Mg2SbO5F2 ceramics sintered above 825 °C was identified by XRD refinement analysis. The microwave dielectric performances of present ceramics were closely correlated with its phase transition process andmicrostructure. Typically, optimal microwave dielectric performances (εr ~ 8.1, τf ~ –54.0 ppm/°C, Q × f ~ 68,500 GHz (under9.2 GHz)) were achieved for 825 °C-sintered Li3Mg2SbO5F2 ceramics. Moreover, a cylindrical dielectric resonator antennafabricated from Li3Mg2SbO5F2 ceramics exhibited a maximum return loss (S11) of –30.3 dB, a maximum gain of 5.3 dB andVSWR of 1.1 at the center frequency of 11.6 GHz, and impedance bandwidth of 300 MHz (at –10 dB), respectively.