Phase formation and microwave dielectric properties of the Pb2+ and Sr2+ doped La4Ti9O24 ceramics were investigated. Using electron diffraction and Rietveld analysis of the X-ray powder diffraction patterns, we show that the increase in the concentration of Pb2+ and Sr2+ doping results in the structural transition from La4Ti9O24 to a La2/3TiO3-type phase (Ibmm, No. 74). A change in the crystalline phase considerably affects the microwave dielectric properties, increasing the epsilon(r) from 37 to 130, reducing Q x f from 25.000 to 5500, and increasing temperature coefficient of the resonant frequency (TCF) from 15 to 300 ppm/degrees C. (C) 2006 Elsevier Ltd. All rights reserved.