The microstructures and the microwave dielectric properties of the (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3 ceramic system were investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. Ca0.6La0.8/3TiO3 has dielectric properties of dielectric constant epsilon(r) similar to 109, Q x f value similar to 17,600 GHz and a large positive tau(f) value similar to 213 ppm/degrees C. (Mg0.95Co0.05)TiO3 ceramics possesses high dielectric constant (epsilon(r) similar to 16.8), high quality factor (Q x f value similar to 230,000 GHz), and negative tau(f) value (-54 ppm/degrees C). As the x value varies from 0.1 to 0.8, (1-x)(Mg0.95Co0.05)TiO(3)xCa(0.6)La(0.8/3)TiO(3) ceramic system has the dielectric properties as follows: 21.55 < epsilon(r) < 75.44, 21,000 < Q x f < 90,000 and -10 < tau(f) < 140. By appropriately adjusting the x value in the (1-x)(Mg0.95Co0.05)TiO3-xCa0.6La0.8/3TiO3 ceramic system, zero tau(f) value can be achieved. With x = 0.15, a dielectric constant epsilon(r) similar to 25.78, a Q x f value similar to 84,000 GHz (at 9 GHz), and a tau(f) value similar to 2 ppm/degrees C were obtained for 0.85(Mg0.95Co0.05)TiO3-0.15Ca(0.6)La(0.8/3)TiO(3) ceramics sintered at 1400 degrees C for 4 h. For practical application in communication systems, it is desirable to be able to sinter at lower temperatures. Therefore, V2O5 was as a sintering aid for lowering the sintering temperature of 0.85(Mg0.95Co0.05)TiO3-0.15Ca(0.6)La(0.8/3)TiO(3) ceramics. At the same time, the 0.85(Mg0.95Co0.05)TiO3-0.15Ca(0.6)La(0.8/3)TiO(3) ceramic system with 0.5 wt% V2O5 can be obtained good properties at the microwave frequencies for 1200 degrees C. (c) 2006 Elsevier Ltd. All rights reserved.