Ceramic dielectrics in the PbO–MgO–Nb2O5 based system, doped with several dopants such as Ti, Co, and Zn, were characterized for their microstructure and composition by transmission electron microscopy (TEM) and energy dispersive x-ray microanalysis (EDS). The ceramics exhibited a microstructure comprised of the matrix and many crystalline inclusions. The inclusions are compositionally enriched with magnesium and a smaller concentration of cobalt. Based on the selected area electron diffraction pattern (SADP) of the inclusion, the calculated interplanar spacings match those of (Mg, Co)O while those of the matrix match those of Pb(Mg0.33Nb0.67)O3. X-ray spectrometry (EDS) does not reveal a PbO phase in the matrix grain boundaries. The matrix exhibits finer features upon prolonged irradiation by the 200 keV electron beam. This does not affect the composition or interplanar spacings even though they exhibit polycrystalline diffraction patterns, and the high resolution micrographs show moiré patterns.