Ni 8 0 Fe 2 0 /Mo magnetic multilayers with a repeat length of 3.4nm have been fabricated using magnetron sputtering. The interdiffusion coefficient D was determined by measuring the intensity of the X-ray satellite peak arising from the modulation as a function of annealing time. As annealing temperature is below 483K, the interdiffusion was found to be relatively slow (D<8.88x10 - 2 5 m 2 /s), in that the Ni 8 0 Fe 2 0 /Mo multilayers have a strong resistance to atomic interdiffusion. The temperature dependence of interdiffusion in the range 343-683K is described by D=4.02x10 - 2 2 exp(-0.26eV/kT)m 2 s - 1 . Compared with the extrapolation of published higher temperature data, the interdiffusion at a temperature of 633K is found to be more rapid, which is suggested to result from moving grain boundaries and coherency strains in the multilyers.