Abstract The dielectric constant of monoclinic zirconia and of lime-zirconia (up to a CaO content of 20% mole) has been measured at 25 °C by the powder method. For pure ZrO2 the D.C. is 13.5, while for lime-zirconia a non linear dependence on the CaO content has been observed in the measured range, with a maximum at about 14% mole CaO. The results are discussed, in the light of the authors previous density data for the same systems, in terms of the width of the homo­geneity range of the solid solutions