The microwave dielectric properties of La(Mg0.5-xCoxSn0.5)O-3 ceramics were examined with a view to exploiting them for mobile communication. The La(Mg0.5-xCoxSn0.5)O-3 ceramics were prepared using the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La(Mg0.4Co0.1Sn0.5)O-3 ceramics revealed that La(Mg0.4Co0.1Sn0.5)O-3 is the main crystalline phase, which is accompanied by small extent of La2Sn2O7 as the second phase. Formation of this Sn-rich second phase was attributed to the loss of MgO upon ignition. Increasing the sintering temperatures seemed to promote the formation of La2Sn2O7. An apparent density of 6.67 g cm(-3), a dielectric constant (epsilon(r)) of 20.3, a quality factor (Q.F.) of 70,500 GHz, and a temperature coefficient of resonant frequency (tau(f)) of -77 ppm degrees C-1 were obtained for La(Mg0.4Co0.1Sn0.5)O-3 ceramics that were sintered at 1550 degrees C for 4 h. (C) 2011 Elsevier B.V. All rights reserved.