Ba0.4Sr0.6TiO3-Mg2TiO4 composite ceramics were fabricated via conventional solid state reaction process. Dielectric properties of the composites were investigated systematically. It was shown that their dielectric constants decreased monotonously from 1197 to 60 with the contents of increasing Mg2TiO4 from 0 to 70 wt%. Tunability had a slight change from 24.0% to 20.5% as the volume fraction of Mg2TiO4 was increased from 0 to 62 vol%. However, it decreased substantially from 20.5% to 13.4% above the threshold from 62 vol% to 71 vol%. Such an obvious change in tunability was well explained by connectivity levels of the binary composites. Q values of the composite ceramics were more than 200 (tg delta < 0.005) at microwave frequencies of less than 10 GHz. Dielectric dispersion was observed at about 22 GHz using interdigital capacitor (IDC) stucture. (C) 2011 Elsevier Ltd. All rights reserved.