Low-temperature (250-397°C) annealing was found to cause a large decrease in the resistivity of radio-frequency sputter-deposited thin (≤ 500 Å) Permalloy films. A transmission electron microscope was used to investigate a probable microstructural change occurring during the annealing. It was found that the low-temperature annealing induced considerable grain growth in these films. Furthermore, an electron diffraction analysis has shown that this grain growth was accompanied by the formation of the ordered phase (Ni3Fe). The use of dark-field imaging revealed that the small ordered region appears to be formed around the disordered regions via a grain-boundary diffusion mechanism. The observed resistivity decrease was proposed to occur by the structural ordering as a result of the annealing. The measured activation energy for this process was 0.72 eV. This activation energy appears to be associated with the grain boundary migration of excess vacancies trapped during film formation.