Fe 1 - x Sn x (0.04 =< x =< 0.124) solid solutions with nanometer-sized grains were prepared by mechanical alloying. Broad spectral components are ascribed to Fe and Sn atoms at grain boundaries (GB) of the as-milled materials. The mean hyperfine fields at the nuclei of atoms at GB are smaller than they are for atoms in grains. By measuring the grain size and the fraction of atoms at grain boundaries, the effective thicknesses of the grain boundaries could be estimated to be ~ 1 nm. Previously-reported Mossbauer spectra of 1 1 9 Sn atoms at GB of coarse-grained iron are discussed.