Electrically conducting oxide thin films, CaxSr1-xRuO3, where x varies from 1 to 0, were prepared by radio frequency (RF) magnetron sputtering, and their structural compatibility with (Ba,Sr)TiO3 thin films was investigated. It was found that both materials crystallize into the perovskite structure, and the lattice parameter for CaxSr1-xRuO3 can be tuned to that of (Ba,Sr)TiO3 by adjusting the Ca/Sr ratio, so that the compatibility between the two materials at the interface is increased. Structural, chemical, and electrical properties of the thin films and the heterostructures were characterized. Cross-sectional high-resolution electron microscopy (HREM) revealed that the (Ba, Sr)TiO3 thin film was grown epitaxially on the (Ca,Sr)RuO3. The potential utility of CaxSr1-xRuO3 as a bottom electrode for (Ba,Sr)TiO3 is suggested.