Microstructural characteristics including ferroelectric domain boundaries, atomic ordering and TiO6 octahedron tilting of Pb1-xCaxTiO3 (x = 0.3, 0.4, 0.5) were studied and correlated to microwave properties. Using transmission electron microscopy, Pb0.5Ca0.5TiO3 specimens reveal 1/2(l 0 0), 1/2(l 10) and 1/2(l 11) extra reflections regularly in electron diffraction patterns. Dark-field images show two different wavy boundaries using different extra reflections, and their contrast characteristics were discussed. High-resolution transmission electron microscopic (HRTEM) images exhibit ordering characteristics with 1/2(l 11) reflections. However, some regions showing no ordering characteristics also exhibit 1/2(l 0 0) and 1/2(l 10) reflections. An octahedron tilting model combined with atomic ordering was constructed to interpret diffraction behavior in Ph1-xCaxTiO3 materials and the relation between microstructures and microwave properties was also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.