Barium titanate (BaTiO
, BT) - potassium niobate (KNbO
, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method using BT and KN nanoparticles. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM), and it was confirmed that two ferroelectric phases, i.e., BT-rich tetragonal and KN-rich orthorhombic phases, always coexisted for all ceramics, which suggested that 0.5BT-0.5KN ceramics had "pseudo- morphotropic phase boundary (MPB)" structure. Thus, the control of the interface area between two phases was important to enhance piezoelectric property. Finally, their piezoelectric property was measured, and the apparent piezoelectric constant d
* increased with increasing interface area.