The effects of R (R = Sm, Pr and La) substitutions for Nd of the (Nd2-xRx)BaZnO5 solid solutions on the crystal structure and microwave dielectric properties were studied, and the lattice parameters of (Nd2-xPrx)BaZnO5 and (Nd2-xLax)BaZnO5 solid solutions were linearly increased with increasing the composition x, whereas those of (Nd2-xSmx)BaZnO5 solid solutions are linearly decreased. The maximum Q(.)f value is obtained when La2BaZnO5 was synthesized, and the microwave dielectric properties are: epsilon(r) = 20.3, tau(f) = -0.9 ppm/degreesC and Q(.)f = 17832 GHz, respectively. (C) 2002 Elsevier Science B.V All rights reserved.