Recently, a new family of piezoelectric perovskite materials, PbHfO3-PbTiO3-Pb(Mg1/3Nb2/3)O3 (PHT-PMN) ternary system was developed, possessing good piezoelectric properties and high Curie temperature near the morphotropic phase boundary (MPB). Nb2O5, as a donor dopant in the perovskite piezoelectric systems has been used to improve the dielectric and piezoelectric properties. In this work, the effect of Nb2O5 addition in the PHT-PMN ternary system was reported. It was found that Nb doping led to the change of phase structure for the PHT-PMN system. With the addition of Nb2O5 content, the ferroelectric polarization was reduced, while the electric-field-induced strain and hysteresis were enhanced significantly. In particular, the 0.2 wt% Nb2O5-doped PHT-PMN exhibited the optimum piezoelectric and electromechanical properties, with d33 and kp being on the order of 670 pC N−1 and of 71%, respectively.