Co2O3 doped BaWO4-Ba0.5Sr0.5TiO3 composite ceramics, prepared by solid-state route, were characterized systematically, in terms of their phase compositions, microstructure and microwave dielectric properties. Doping of Co2O3 promoted grain growth, reduced Curie temperature and broadened phase-transition temperature range of BaWO4-Ba0.5Sr0.5TiO3, which were attributed mainly to the substitution of Co3+ for Ti4+ at B site in the perovskite lattice. Dielectric diffusion behaviors of the composite ceramics were discussed. The composite ceramics all had dielectric tunability of higher than 10% at 30 kV/cm and 10 kHz, with promising microwave dielectric properties. Specifically, the sample doped with 0.2 wt.% Co2O3 exhibited a tunability of 20%, permittivity of 225 and Q of 292 (at 1.986 GHz), making it a suitable candidate for applications in electrically tunable microwave devices. (C) 2010 Elsevier Ltd. All rights reserved.