A color reaction for panaxadiol, an artifact sapogenin produced by acid hydrolysis from saponin of Ginseng root (root of Panax ginseng C. A. Meyer), and for Ginseng saponin mixture containing glycosides of protopanaxadiol, a genuine sapogenin, is described. A red-purple color product of panaxadiol or Ginseng saponin was formed by beat treatment with vanillin and sulfuric acid. The red-purple color was stable for two hours in an ice-cold water bath and had a visible absorption maximum at 544 nm. The relationship between absorbance at 544 nm and quantity of both panaxadiol and Ginseng saponin preparation followed Beer's law for 20 μg to 100 μg of panaxadiol and 50 μg to 250 μg of Ginseng saponin.