Tetraarsenic Tetrasulfide (also known as Realgar, "ruby sulfur" or "ruby of arsenic") is an arsenic compound with antitumor activity, especially in acute promyelocytic leukemia that is resistant to retinoic acid. Tetraarsenic Tetrasulfide is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment. Tetraarsenic Tetrasulfide is in wide use in traditional Chinese medicine. Early clinical exploration of Tetraarsenic Tetrasulfide for the treatment of AML and CML started in the 1960s and suggested that Tetraarsenic Tetrasulfide was a potent agent for leukemia treatment. Recently, a single-center pilot study demonstrated that Tetraarsenic Tetrasulfide treatment was effective and convenient for treating low-risk acute promyelocytic leukemia patients. Based on these clinical achievements, Tetraarsenic Tetrasulfide has been approved by the China Food and Drug Administration and recommended as a second-line chemotherapeutic agent for the treatment of acute promyelocytic leukemia in China