A high-temperature anelastic relaxation peak in the mechanical loss spectrum of 18-carat yellow gold polycrystals is analysed and interpreted as due to grain boundary sliding accommodated predominantly by elastic deformation of the grains. The characteristic time scale of the relaxation process tvaries with the grain size d, and the grain size exponent is found to be m = 1.09 +/- 0.10 which is in perfect accord with the Zener model that attributes a grain boundary relaxation to viscous sliding along the grain boundaries. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.