The microwave dielectric properties of CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O-3 ceramics were investigated with a view to their application in microwave devices. CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O-3 ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of CuO-doped La2.98/3Sr0.01(Mg0.5Sn0.5)O-3 ceramics exhibited no significant variation of phase with sintering temperature. By adding 0.75 wt.% CuO, a dielectric constant of 20.07, a quality factor (Q x f) of 63,000 GHz, and a temperature coefficient of resonant frequency tau(f)(-77.0 ppm/degrees C) were obtained when La2.98/3Sr0.01(Mg0.5Sn0.5)O-3 ceramics were sintered at 1500 degrees C for 4 h. (C) 2011 Elsevier B. V. All rights reserved.