The electromechanical and electric-field-induced strain properties of xPb(Yb1/2Nb1/2)O-3.yPbZrO(3).(l-x-y)PbTiO3 (x = 0.12, 0.25, 0.37; y = 0.10-0.40) ceramics have been studied systematically as a function of Pb(Yb1/2Nb1/2)O-3 (PYN) content and PbZrO3/PbTiO3 (PZ/PT) ratio. In addition, the effect of MnO2 on the electromechanical properties of 0.12Pb(Yb1/2Nb1/2)O-3.0.4OPbZrO(3).0.48PbTiO(3) was also investigated. The maximum transverse strain values of 1.6 X 10(-3) for x = 0.12, 1.45 X 10(-3) for x = 0.25, and 1.36 X 10-3 for x = 0.37 were obtained at the compositions which were regarded as the morphotropic phase boundary (MPB). The transverse strain was maximized at the AIPB composition. The value of the maximum electromechanical coupling coefficient was 0.69 for y = 0.40 and x = 0.12 composition. In the 0.12Pb(Yb1/2Nb1/2)O-3.0.4OPbZrO(3).0.48PbTiO(3) composition, the temperature of the maximum dielectric constant decreased and the grain size increased with an addition of MnO2. The electromechanical coupling coefficient decreased while the mechanical quality factor rapidly increased with an addition of MnO2. These resulted mainly from the acceptor effect of manganese ions that were produced by doping MnO2 into the perovskite structure.