The perovskite structure of Pb (Zn1/3Nb2/3)O3 (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb (Zr0.47Ti0.53) O3 (PZT) across the morphotropic phase boundary (MPB). The 0.5 PZN-0.5 PZT specimen was found to have a two-phase zone, having a high piezoelectric coefficient, d33 (430 pC/N), an electromechanical coupling factor, kp (0.67), a field-induced strain, S (0.24% at 2 kV/mm), and a remnant polarization, Pr (27μC/cm2). A phase transition from a rhombohedral to tetragonal phase occurred when a relatively low electrical field was applied to the specimen. This transformation occurred only when the rhombohedral phase coexisted with an equal amount of the tetragonal phase of the perovskite structure. Small rhombohedral domains, which were present around the relatively large tetragonal domains, transformed as a result of the applied field. The excellent electromechanical properties at the MPB composition are attributed to this phase transition in the PZN based ceramics.