Radiation-enhanced diffusion is one of the most important parameters for the understanding and modeling the effect of radiation on materials. In this study, the average effective interdiffusion coefficients of Ni and Cr in pure iron, an Fe-15Cr-15Ni model alloy and a modified 316 stainless steel for fuel subassembly of FBR were evaluated under neutron irradiation by using “miniature diffusion couples” which were electroplated with Ni or Cr. The miniature diffusion couples were irradiated in the experimental fast reactor JOYO at temperature ranging from 400 to 550°C for 4 220 hours, to doses between 1.4 and 14 dpa. The interdiffusion was enhanced by irradiation. In particular, Ni diffusion increased by several orders of magnitude. The enhancement of diffusion depends on the point defect flux, which is affected by solute elements and the microstructure development under irradiation.