The microwave dielectric properties and the microstructures of MgNb2O6 ceramics with CuO additions (1-4 wt.%) prepared with conventional solid-state route have been investigated. The sintered samples exhibit excellent microwave dielectric properties, which depend upon the liquid phase and the sintering temperature. It is found that MgNb2O6 ceramics can be sintered at 1140 degreesC due to the liquid phase effect of CuO addition. At 1170 degreesC, MgNb2O6 ceramics with 2 wt.% CuO addition possesses a dielectric constant (epsilon(r)) Of 19.9, a Q x f value of 110,000 (at 10 GHz) and a temperature coefficient of resonant frequency (tau(f)) of -44 ppm/degreesC. The CuO-doped MgNb2O6 ceramics can find applications in microwave devices requiring low sintering temperature. (C) 2003 Published by Elsevier Science Ltd.