Self-diffusion studies were performed on high-density n-Fe specimens prepared by the compaction of gas-condensed nanocrystallites at elevated temperatures. The self-diffusion coefficients determined assuming a type C diffusion process are similar to or slightly higher than the values estimated for the conventional GB diffusion by extrapolating high temperature diffusion data to lower temperatures. The time-dependent decrease of the apparent selfdiffusivities is probably due to structural relaxation of the interfaces and to interface migration effects. According to the measured D values, however, we presume that the nature of GBs in high-density n-Fe is similar to that in conventional poly-Fe.