X-ray diffraction analysis of Yung-Sa, an inorganic chinese drug in Korea, revealed the following: 1. "Yung-Sa" is red mercuric sulfide crystal (Vormillion) which is cinnabar type of hexagonal system. 2. It is accurate to call "Yung-Sa" synthetic red mercuric sulfide. 3. "Chung-Sa-Du" is mixture of crystals of cinnabar and meta-cinnabar types.