In the application of tuneable microwave devices of ferroelectric (BaSr) TiO3 systems the two critical parameters needed for optimal device performance are high tunability and low dielectric loss. The dielectric loss of the materials is strongly dependent on microstructure. This paper is concerned with an investigation of the variation in the dielectric and mechanical losses in BaxSr1-xTiO3 systems (x = 0.5, 0.6, 0.7 and 1.0) with microstructure (grain sizes from 1 mum to 50 mum). The magnitude of the loss peak and sharpness of the anomaly in the dielectric constant/elastic modulus observed for the phase transitions in BaxSr(1-x)TiO(3), depend not only on the composition and but also on the grain size. A relaxation peak has been observed in large grain material, which is indication of interactions between different configurations of domain walls and the diffusion of oxygen vacancies in the domains.