Abnormal grain growth (AGG) during the sintering of Pb(Mg-1/3 Nb-2/3)O-3-35 mo1% PbTiO3 was investigated. When a small amount of SiO2 was added, large abnormal grains with the penetration twin characteristic were observed to appear. AGG, in this case, is because of the twin plane re-entrant edges that provide coarsening advantage. When TiO2 was added, on the other hand, the abnormal grains were simple cubic in morphology with well-developed {100} planes. In this case, the coarsening advantage is suggested to be because of grain boundary re-entrant edges.