Undoped and ZrO2 doped (0.5, 1.0, 2.0, 3.0 wt.%) Ba0.55Sr0.45TiO3/MgO composites were prepared by traditional ceramic processing. The ZrO2 doping effect on the structural, surface morphological, tunability and dielectric properties were systemically investigated. The result shows that the tunability of Ba0.55Sr0.45TiO3/MgO composites was improved by using ZrO2 dopant. The Ba0.55Sr0.45TiO3/MgO composite with 1.0 wt.% ZrO2 dopant exhibits high tunability (17% at 2.5 kV/mm), low dielectric constant (200) and a low microwave loss (0.005, 2.7 GHz), which are suitable for microwave tunable application. (C) 2006 Elsevier Ltd. All rights reserved.