Studies on lattice change of a nickel-phosphorus amorphous alloy were carried out using not only high temperature X-ray diffraction but also extended X-ray absorption fine structure (EXAFS) analysis. Their thermal properties were characterized by differential scanning calorimetry (DSC). Since the results suggested that lattice relaxation occurred in the amorphous state by annealing, EXAFS measurements were carefully performed for characterizing the local structure of the amorphous alloys. The EXAFS analysis showed that the local structures around Ni atoms, which may be the Ni-Ni and Ni-P correlation, were changed by annealing. High temperature X-ray diffraction showed that small amount of crystal phase appeared by annealing up to 820 K, while clear diffraction peaks of Ni3P were observed above 1100 K. These micro/nanoscale structural changes did not correspond to that obtained by DSC which showed an exothermic reaction of atomistic reordering at 630 K. We need analysis of the nanostructures by small angle X-ray scattering or a high resolution transmission electron microscope.