Inorganic nanoparticles made of inorganic materials are difficult to arrange in an ordered manner and form higher-order structures by themselves. However, surface modification with DNA, which has selective binding properties, as a guiding molecule can control the interaction and binding between nanoparticles to assemble them into desired crystal structures. In this report, the author presents recent work on determining the structural conditions for DNA-functionalized nanoparticle superlattices that can maintain crystalline symmetry not only in the hydrated state but also after drying by precisely characterizing crystallinity using small-angle X-ray scattering.