By successfully fabricating dense Ba0.70Sr0.30TiO3 ceramics in the size range of 0.1—10 μm，the grain size dependence of the Curie temperature TC，dielectric constant in ferroelectric phase εF and in peak εM were systematically investigated. The results show that TC will not decrease considerably until the grain size becomes small enough. This can be explained by Buesseums internal stress model. As the grain size increases，εF increases first and decreases afterward，which can be interpreted by Shaikhs series-parallel model. The main active factors are internal stress，domain and grain boundary. On the other hand，if the grain size is small，εM increases first and decreases afterward as the grain size increases. If the grain size is bigger，εM increases slightly. This can be explained by the diffuse phase transition theory and series-paralled model. The main active factors are grain boundary，internal stress，for small grain sizes, and domain and grain boundary for bigger grain sizes，respectively.