In order to trace the reaction sequence during conventional solid-state reaction in BaO-xSm(2)O(3)-4.5TiO(2) (0.0 less than or equal to x less than or equal to 1.25) system, of which the phase development process is not clearly known, different barium sources of BaCO3 and BaTiO3 were used as starting materials. From the analysis of X-ray powder diffraction (XRD) patterns, different secondary phases could be identified depending on the barium source used, which might mean that the equilibrium phases in BaO-xSm(2)O(3)-4.5TiO(2) system are very difficult to be synthesized. When BaTiO3 was used as a raw material, because the precursor provides short diffusion paths of ions, the system revealed less secondary phases that was considered to be closer to the equilibrium state. The microwave dielectric properties of the sample used BaTiO3 showed superiority accordingly. Microstructure and dielectric properties were examined and discussed in terms of secondary phase development. (C) 2002 Elsevier Science B.V All rights reserved.