The influence of the morphotropic phase boundary (MPB) on the dielectric and piezoelectric properties of PbNi1/3Nb2/3-PbZrO3-PbTiO3 (PNN-PZ-PT) ternary system were systematically investigated. The results showed that the piezoelectric constant d(31) and plane coupling factor k(p) reached a maximum in the vicinity of morphotropic phase boundary. The highest value of the piezoelectric constant d(31) was 260 x 10(-12) C/N. The Curie temperature T-c decreased rapidly with increasing content of PNN. The lattice parameters a increased and c decreased with increasing PNN content and the Zr/Zr + Ti ratio as a result of the crystal structural transformation from tetragonal to rhombohedral phases.