8-Mercaptoquinoline is the organosulfur compound with the formula C9H7NSH. It is a derivative of the heterocycle quinoline, substituted in the 8-position with a thiol group. The compound is an analog of 8-hydroxyquinoline, a common chelating agent. In terms of physical properties, this compound crystallizes as a red solid dihydrate but the anhydrous compound is a blue liquid.