Zeolites, which are microporous aluminosilicates, have excellent properties, such as water absorption ability, ion exchange capacity, molecular sieving ability and catalytic ability. The crystal structure is composed of TO4 tetrahedra (T = Si, Al) that share each oxygen atom to form n-membered rings. Although zeolites are basically crystalline solids, heating treatment (HT) collapses the crystal structure, turning them into amorphous solids. Rietveld refinement is generally used to characterize crystal structures, but it is not applicable to amorphous materials due to the broadness of the peaks, called halos. However, PDF analysis can derive structural information from amorphous material, thereby solving this problem.