Real-time direct observation of ferroelectric domains and phases under electric-field poling along [001] at room temperature in Pb(Mg1/3Nb2/3)(0.67)Ti0.33O3 (PMNT33%) single crystal has been performed by polarizing microscopy. A hysteresis loop of polarization vs. electric field at room temperature was also measured for comparison. By using relations of crystallographic symmetry and optical extinction, polarizing microscopy reveals orientations of the domain polarizations and their corresponding phases. It also provides direct real-time observation of microcracking phenomena. It was found that the monoclinic phase domains play a crucial role in bridging higher symmetry (tetragonal and rhombohedral) phases while field-induced phase transitions take place. (c) 2006 Elsevier B.V. All rights reserved.