The microwave dielectric proper-ties of the complex perovskite ceramics with compositional variation of the A-site cations were closely related to bond valence of the A-site cations as well as ionic polarizability. As the bond valence of the A-site cations decreased, the cations of the A-site behaved like the rattling cation. The temperature coefficient of the resonant frequency of the complex perovskite ceramics also was associated with the bond valence of the A- and B-site cations as well as the tolerance factor. (C) 2002 Elsevier Science B.V. All rights reserved.