It has been found that Pb1-yKy(Zn1/3Nb2/3)O3-y/2 ceramic compounds are of the rhombohedral perovskite-type for y>0.10. The solid solutions of xPb0.9K0.1(Zn1/3Nb2/3)O2.95–(1-x)PbTiO3 were studied as piezoceramic materials over the whole system. The structure, and dielectric as well as piezoelectric properties were examined on these ceramic compositions. The investigation of the piezoelectric properties in this system showed the planar coupling factor kp, to be highest near the rhombohedral-tetragonal phase boundary at x=0.88 while the mechanical quality factor Qm comes to its minimum value just on the rhombohedral side (x=0.90) of the transition and takes a little high values in the tetragonal field. However, the dielectric constant ε33T decreases and the spontaneous polarization Ps increases monotonically with the increase of PbTiO3.