The colossal piezoelectric effect of relaxor-based ferroelectrics has attracted much attention due to the technological importance of the conversion between electric and mechanical energies. The mechanism of the significant field effect on piezoelectric properties in this disordered system has become one of the current topics in pure and applied physics. The important key factor in the understanding of relaxors is polar nanoregions (PNRs) which appear at temperatures far above the dielectric maximum or Curie temperature. PNRs play a dominant role in the formation of unique characteristics of relaxors and are regarded to be caused by spatial and dynamic heterogeneity. However, a detailed microscopic picture of their evolution depending on temperature or electric field is still the subject of controversy. The elastic and dynamical properties of the Pb(B1/3B'(2/3))O-3-type relaxor-based ferroelectrics and their solid solutions with pure ferroelectrics have recently been studied extensively by the broadband micro-Brillouin scattering spectroscopy (BMBS) to clarify the role of PNRs. This paper reviews the recent progress in the understanding of fast dynamics of PNRs of typical relaxor-based ferroelectrics of (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) and (1-x)Pb(Zn1/3Nb2/3)O-3-xPbTiO(3) in the gigahertz frequency range achieved by using BMBS. (C) 2011 Elsevier B. V. All rights reserved.