Undoped and La(2)O(3)doped (0.5, 1.0, 2.0, 3.0 wt.%) Ba0.55Sr0.45TiO3/MgO composites were prepared by traditional ceramic processing and their structural, surface morphological, tunable properties and their dielectric properties at low frequency and microwave frequency were systemically examined. The result shows that La2O3 dopant has a strong effect on the average grain size. The La2O3 doped samples have lower temperature coefficient of capacitance than the undoped. The 0.5 wt.% La2O3 doped sample has a little higher tunability than the undoped and the tunability of other doping concentration samples is lower as compared to the undoped. The addition of La2O3 decreases the dielectric constant and increases quality factor (Q x f) at microwave frequency. The 0.5 wt.% La2O3 doped samples have the best properties among these samples and have a higher tunability, lower dielectric constant and lower dielectric loss tangent at microwave frequency and these properties are very beneficial to the development of the tunable devices application. (c) 2005 Elsevier B.V. All rights reserved.