Two new cation-deficient hexagonal perovskites Ba4LaMNb3O15 (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba4LaTiNb3O15 has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (tau(f)) +93 ppm degreesC(-1) at room temperature; Ba4LaSnNb3O15 has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and tau(f) -29 ppm degreesC(-1). (C) 2004 Elsevier Ltd. All rights reserved.