The effects of V 2 O 5 and Li 2 CO 3 on the sinterability and microwave dielectric properties of Mg 4 Nb 2 O 9 (MN) ceramics were investigated. With addition of 1.5wt% V 2 O 5 , the dielectric constant (e) and Q · ƒ value of MN ceramics sintered at 1,000°C are comparable to those of pure MN sintered at 1,400°C. The good results are because of the enhancement of the density by liquid sintering at the lower temperatures. With the mixtures of V 2 O 5 and Li 2 CO 3 , the sintering temperature of MN was further reduced to 925°C at the expense of the quality factor (Q · ƒ) value. Typically, e of 13.7 and Q · ƒ value of 78,000 GHz were obtained for the specimens with mixtures of 1.5wt% V 2 O 5 and 1.5wt% Li 2 CO 3 and sintered at 925°C for 5 h.