Crystallization of amorphous metallic alloy Fe95Si5 (at. %) was investigated using X-ray diffraction measurements performed in-situ during isothermal annealing. Fe95Si5 ribbons, prepared by melt-spinning, have been analyzed by differential scanning calorimetry (DSC). Their nanostructural evolution has been studied by combining heat treatments with conventional X-ray diffraction. The objective of the experiment was to determine changes in the structural parameters during crystallization of the examined alloy. The crystalline diameter and the lattice constant of the crystallizing phase were used as parameters to evaluate structural changes in the material.