A-site deficient perovskites received wide interest due to their attractive dielectric properties. The structural evolution of a A-site deficient perovskite La(1-x)/3NaxNbO3 (0.0 < x <= 0.4) and their microwave dielectric properties (0.0 < x <= 0.20) have been studied by X-ray diffraction (XRD), scan electron microscopy (SEM) and microwave resonant measurement in this paper. All sintered samples exhibited single phase and dense microstructure. The symmetry of the crystal structure at room temperature changed from orthorhombic (x <= 0.2) to tetragonal (x = 0.25) and finally into the cubic (0.25 < x <= 0.4). The A-site ordering degree decreased with the increase of sodium content and became disorder when x > 0.25. The dielectric permittivity and temperature coefficient of resonant frequency (tau(f)) value linearly increased with the increase of sodium content due to the decrease of tilting angle of NbO6-octahedron. The quality factor (Q x f) decreased with increasing sodium content, which was mainly due to the decrease of A-site ordering. (C) 2010 Elsevier B.V. All rights reserved.