The use of single crystals for crystal structure analysis is a common practice. However, it is difficult to apply crystal structure analysis to samples where it is hard to isolate the crystalline pure substance, or for samples that are difficult to crystallize even if a pure substance is obtained. It is becoming possible to perform crystal structure analysis on powder samples if a pure crystalline substance can be obtained. This progress is due to recent increases in the calculation speed of personal computers and significant developments in analysis software, as well as improvements in the precision of powder X-ray diffractometers. In this example, identification of impurities was performed using the diffraction profile of a powder cocrystal sample with impurities. The remaining diffraction peaks were used for indexing, structure determination, and structure refinement.