ChemInform Abstract The carbon reduction of BaSO4 yielding BaS besides small amounts of BaCO3, SO2, Sn, and COS, is found to proceed via the formation of intermediate barium sulfite. Above 500 rc C, BaSO3 decomposes mainly to BaSO4 and BaS and, to a low xtent, to BaO and SO2. A series of consecutive and side reactions is proposed describing the stepwise reduction of BaSO4 to BaS.