Grain boundary diffusivities of a110Ag radioactive tracer have been measured in polycrystalline Pb specimens over a temperature range of 57–118 °C. Diffusivity parameter values are expressed by the Arrhenius relation:P(cm3 s−1)=Dgb&dgr;&agr;=1.58×10−4×exp(−41120 J mol−1/RT). These values are five orders of magnitude higher than those relative to self‐grain boundary (gb) diffusivity of lead. Thus, the difference between silver and lead grain boundary mass transport is almost the same as that measured for bulk diffusion. The possible explanations for such a similarity are discussed in relation with the particular bulk diffusion mechanism of silver and a possible high grain boundary segregation of this solute.