Abstract: Ages of some Palaeozoic stratigraphic units in Southern Mongolia are revised by means of conodont study. The Arynshand Formation should be the Early Carboniferous. The upper part of the Gavuu Member of the Mandalovoo Formation near the Bayan-Khoshuu Ruins section in the Mushgai area is definitely the earliest Devonian; a new stratigraphic unit, the Olonovoot Formation, is suggested for this part. The upper part of the Tsagaanbulag Formation at the Tsakhir Section and the Ulaan-Shand Section should be assigned to the Lochkovian rather than Silurian. The Chuluun Formation is actually late Emsian, and the Tsagaankhaalga Formation is Early Eifelian. The Indert Formation is Early Carboniferous.

Key words: Palaeozoic, Conodonts, Arynshand Formation, Gavuu member, Tsagaanbulag Formation, Chuluun Formation, Tsagaankhaalga Formation, Southern Mongolia