To investigate the possibility of their application to both high density dynamic and nonvolatile ferroelectric random access memories, heteroepitaxial BaxSr1-xTiO3 (BSTO) thin films with various Ba content from x=0 to 1. 0 were prepared on conductive SrRuO3 electrode films, and the crystallographic, dielectric and ferroelectric properties were investigated. The compositional phase boundary between paraelectric and ferroelectric phase at room temperature was located at about x = 0. 12 in the heteroepitaxial films, indicating a quite different composition to that of the bulk (x = 0. 70). At this composition of x = 0. 12, the dielectric constant attained the maximum value of 740 for the BSTO film with a thickness of 77 nm. The composition with a lager Ba content (x 0. 32) showed ferroelectricity at room temperature. The maximum value of remanent polarization of 2Pr = 0. 38 C/m2 was obtained at the composition of x = 0. 70 in this study.