The microwave dielectric properties and microstructures of Ba(Mg 1/3Ta 2/3)O 3 (BMT) ceramics sintered at low temperatures with 2–3 wt.% NaF additives were investigated. BMT ceramics sintered at 1340 °C for 3–12 h showed dielectric constants ( ε r ) of 25.5–25.7, Qf values of 41 500–50 400 GHz and temperature coefficients of the resonator frequency ( τ f ) of 10.9–21.4 ppm °C −1. The variation of sintering time almost had no effect on the dielectric constant. The Qf value increased and the τ f decreased with increasing sintering time. The ordering degree of Mg 2+ and Ta 5+ at B-sites increased with increasing sintering time.