A new technology was adopted to prepare Ba(Mg1/3Ta2/3)O3 powder by using Ta2O5•nH2O nano-particles as base material and magnesiumcitrate, barium citrate solutions as coating phase through the liquid-phase coating interfacial reaction. The product was investigated by useof TG, DTA, XRD and TEM analysis. The results show that approximately spherical Ba(Mg1/3Ta2/3)O3 particles with high purity and goodsintering activity can be synthesized at about 800 ◦C, the diameter is 20–30 nm. After sintering at 1400 ◦C for 4 h, the as-prepared BMTceramics show grains of 2–5_m and about 95.1% of the theoretical density. Preliminary microwave dielectric measurements reveal that thedielectric constant and the unloaded Q of the ceramics are 24.9 and 8792, respectively, at about 8 GHz.