The crystal structure and microwave dielectric properties of the (Sm1-xYx)(Ti1.5W0.5)O-6 (x = 0 and 0.5) ceramics sintered at 1375 degrees C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm0.5Y0.5)(Ti1.5W0.5)O-6 ceramic sintered at 1400 degrees C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h. (c) 2007 Elsevier Ltd. All rights reserved.