The microstructure evolution of Pb(Mg1/3Nb2/3)O3 –PbTiO3 (PMN-PT) based ceramics has been investigated to determine the influence of the presence of PbO content in excess of stoichiometric values. The microstructure of the different materials showed a different evolution of secondary phases (free PbO and pyrochlore type) related to the PbO excess. The pyrochlore phase appeared in a layer near the top surface of the specimens. The thickness of the layer and the grain size of this secondary phase increased with the amount of PbO excess. A transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. The shell of these grains was Ti-rich PMN, and it is related to the presence of a liquid-phase-assisted sintering mechanism.