The synthesis and microwave dielectric characterization of (Nd2-xLax)BaZnO5 solid solutions were studied. The samples obtained were single phase over the whole composition range and the lattice parameters of solid solutions were linearly increased with increasing the composition. Moreover, the expansion of the volume in the RO8 (R = Nd and La) and BaO10 polyhedra and ZnO4 tetrahedron were recognized when Nd ions were substituted by La. These variations in the lattice parameters and volumes of the polyhedra are basically attributed to the differences in ionic radii between Nd3+ and La3+ ions. From the evaluation of microwave dielectric properties, it was shown that the appropriate tau(f) values ranging from 4.6 to -5.0 ppm/degreesC are obtained by La substitution for Nd ion, and the highest Q(.)f value was 17,832 GHz at x = 2. (C) 2002 Elsevier Science Ltd. All rights reserved.