La modified Pb(Mg1/2W1/2)O-3 were prepared by solid-state reaction process, and the sintering behavior, microstructure and microwave dielectric properties were investigated by X-ray powder diffraction (XRD), Raman scattering and HP network analyzer in this paper. A series of single phase perovskite type solid solutions with A-site vacancies (Pb1-3x/2Lax(Mg1/2W1/2)O-3 (0 less than or equal to x less than or equal to (2/3))) were formed. The solid solution took cubic perovskite type structure (Fm3m) with random distribution of A-site vacancies when 0 less than or equal to x less than or equal to 0.5, and tetragonal or orthorhombic structure with the ordering of A-site vacancies when 0.5 less than or equal to x less than or equal to 2/3. The dielectric constant and temperature coefficient of resonant frequency decrease with increasing La content. Relatively good combination microwave dielectric properties were obtained for x = 0.56: epsilon(r) = 28.7; Q x f = 18098; and tau(f) = -5.8 ppm/degreesC. (C) 2004 Elsevier Ltd. All rights reserved.