The grain-boundary diffusion (GBD) of 5 9 Fe in pure and in Cr-, Fe- and Zr-doped Ni 3 Al alloys was studied at temperatures between 873 and 1273K using the serial sectioning method. The grain-boundary diffusivities P (P is a product of grain-boundary width δ, and the diffusion coefficient in the grain-boundary D b ) were obtained from the penetration profiles using both the Le Claire's analysis and direct fit of Suzuoka's solution. The activation enthalpies of 5 9 Fe GBD were somewhat lower in comparison with analogous values for 5 1 Cr GBD, reported in our previous paper.