2-Amino-3-mercaptoquinoxaline was prepared by the reaction of 2-amino-3-chloroquinoxaline with thiourea or potassium hydrogensulfide, 2-amino-3-hydroxyquinoxaline with phosphorus pentasulfide, or 2, 3-dimercaptoquinoxaline with ammonia. 2-Substituted thiazolo [b] quinoxaline was prepared by boiling 2-amino-3-mercaptoquinoxaline with excess of acid anhydride or by heating with excess of acid chloride in pyridine.