There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO3 ceramics have a dielectric constant (epsilon(r)), high quality factor (Q) and a small temperature coefficient of resonant frequency (tau(f)). However, basic properties such as its crystal structure,. temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb1-xCax)(Zr1-ySny)O-3 ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from -150-350 degrees C. The phase transformation was ana lysed from high and low temperature XRD data.