Enlarged polymorphic phase transition boundary was observed in the ternary component 0.8Ba 1−x Ca x TiO 3 –0.1BaTi 0.8 Zr 0.2 O 3 –0.1BaTi 0.9 Sn 0.1 O 3 ceramics. The polymorphic phase transition existed at considerable compositions (x=0.005–0.04) and was bounded by the orthorhombic and tetragonal phases. More importantly, enhanced piezoelectric constant d 33 =420pC/N was obtained in the region of polymorphic phase transition. Our work may provide a new guide for designing excellent piezoelectric materials by enlarging polymorphic phase transition boundary.