Piezoelectric and dielectric properties as functions of x and y mole ratio in yPb(ZrxTil-x)O$_3$(1-y)Pb(Mn$\_$1/3/Nb/2/3/)O$_3$, ceramics, PZT-PMN, are investigated for large displacement piezoelectric devices. From the experimental results, when y is 0.95 and x is 0.505, the piezoelectric and dielectric properties are maximum, that is, electromechanical coupling coefficient(kp), piezoelectric strain constant(d$\_$33/), permittivity($varepsilon$$\_$33/$^$T//$varepsilon$$\_$0/), and Curie temperature are 58 %, 272 pC/N, 1520 and about 350$^{circ}C$, respectively. Also, when y is 0.90 and x is 0.50, their properties are 56 %, 242 pC/N, 1220, and 290$^{circ}C$, respectively. As MgO dopant is added from 0 wt% to 1 wt%, kp increases to 63 % and Qm decreases to 500 at the MgO dopant of 0.1 wt%, and then kp decreases to 57 % as MgO is added.