Abstract: The phenomenon of "blood-losing" in chicken-blood stone is mainly due to Fe, Zn and Se. Under oxidation condition, these elements will react with Hg and S which are absorbed in cinnabar particles to produce black cinnabar. This makes the colour of "blood" become darker and darker(so called "blood-losing"). After weathering, the primary chicken-blood stone deposit loses Fe, Zn, Se, ect, owing to leaching of the acid fluid. It makes Hg change into red cinnabar easily, thus the colour of "blood" becomes more stable and brighter, uneasy to lose "blood".