The principle problem in single crystal X-ray analysis is the so-called “phase problem”; however, in the current situation in which various measurement devices, synchrotron radiation facilities and sophisticated software have become available, the largest bottleneck in practice is the acquisition of single crystals, that is, crystallization of the substance to be analyzed. Crystallization is particularly difficult for biomacromolecules. For ribosome, the largest asymmetric single molecule analyzed to date, acquisition of crystals yielding low-resolution diffraction was first reported in 1980, but crystals diffracting to a practical resolution could not be obtained for more than two decades. One of the reasons that it took so long was that only a limited number of researchers had addressed this challenge, as ribosome crystallization had been initially considered an unfeasible task. This was because ribosome was believed to have multiple subtypes and was thus low in homogeneity. If the homogeneity could be evaluated before crystallization, more researchers might have attempted ribosome crystallization to achieve successful ribosome crystallization a few years earlier. This article describes small-angle X-ray scattering from solution-state protein samples and its relevance to evaluation of protein crystallizability.