A microwave dielectric composition, comprising a basic composition, represented by the following formula:(Pb(1-x)Ca(x))(Zr(1-y)Sn(y))O(3)wherein x and y are molar ratios in the relation of 0.15<x<0.40 and 0.15<y<0.50, and a sintering aid represented by the following formula:a ZnO+b Sb.sub.2 O.sub.3wherein a and b are percentages relative to the total weight of the basic composition, in the relation of 0<a+b<0.05 weight %. The composition can be sintered at relatively low temperature and are superior in dielectric constant and quality factor. The low-temperature sintering yields the effects of allowing the sinters to have a fine structure and be of high long-term reliability, including high-temperature resistance and humidity resistance.