When Pb(Mg1/3Nb2/3)O-3 (PMN) with 40 wt% excess PbO is sintered at 1050 degrees C, the grains grow normally and have flat {100} surface segments with round edges. As PbTiO3 (PT) is added up to 8 mol%, the grain growth is still nearly normal, characterized by time invariant normalized size distributions, but the grain edges become more sharply curved. This normal growth behavior is consistent with relatively small surface step free energy as indicated by the round grain edges. As the PT content is increased above 10-35 mol%, the grain edges become sharp and abnormal grain growth occurs. This is consistent with the step free energy increasing with the PT content as indicated by the sharpening grain edges.