Lead-free (Ba-1 Ca-x(x))(Ti0.96Sn0.04)O-3 (BCST) (x=0-0.04) ceramics were prepared using solid-state reaction technique. At room temperature, a polymorphic phase transition from orthorhombic phase to tetragonal phase was identified in the composition range of 0.01 <= x <= 0.03. Extremely high piezoelectric coefficient of d(33)=510pC/N and high planar electromechanical coupling factor of k(p)=48% were obtained for the BCST ceramics at x=0.02. These results indicate that the BCSTs are promising candidates for the widely used lead-based piezoelectric materials.