This work studies the relationship between ferroelectric properties and structural features of the (Pb1-yCay)(Zr0.8Ti0.2)O-3 system with y = 0.0, 0.02, 0.05 and 0.1. All of the samples were prepared by hot-pressing of PZT calcined powder, prepared by conventional ceramic route. Single phase compositions of rhombohedral ( RH) structure were observed for the whole series of the samples studied in this work. However, a linear decrease of RH lattice constant a(p) is seen with increasing the Ca2+ concentration with a subsequent decrease of lattice strain expressed by (90 - alpha(p)). Further, a sharp decline is also observed in the magnitudes of saturation polarization (P-s) of the samples doped with 2 mol% Ca2+. However, the rate of decrease slows down for Ca2+ concentrations above this level. A diffuse phase transition was observed in the case of 10 mol% Ca2+-doped PZT(0.8) which is believed to be possibly due to the distribution in coupling strengths created from a random compositional fluctuations of Ca2+ and Pb2- ions on A-sites. The results are interpreted on crystal-chemical grounds. It is proposed that the long range coupling of (Zr/Ti)O-6 coordination octahedra and Pb2+ ions, due to the covalency of the Pb-O bond, is interrupted by the incorporation of Ca2+. By considering the effect of calcium on coupling strength and coupling distribution, the observed dielectric response for the above compositions is qualitatively explained. (C) 2003 Kluwer Academic Publishers.