(5 - x)BaO-xMgO-2Nb(2)O(5) (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO3, MgO, and Nb2O5 was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 degrees C. The formation of (BaMg)(5)Nb4O15 was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg1/3M2/3)O-3 was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 T. We produced 5MBN ceramics with these dielectric properties: epsilon(r) = 36.69, Qf = 20,097 GHz, and tau(f) = 61.1 ppm/degrees C, and 10MBN ceramics with these dielectric properties: epsilon(r) = 39.2, Qf = 43,878 GHz, and tau f = 37.6 ppm/degrees C. The reaction-sintering process is a simple and effective method for producing (5 - x)BaO-xMgO-2Nb(2)O(5) ceramics for applications in microwave dielectric resonators. (C) 2006 Published by Elsevier Ltd.