An incomplete skeleton of a theropod dinosaur, Bagaraatan ostromi gen. et sp. n., was found in the Nemegt Fm. at Nemegt, Mongolia. The mandible in B. ostromi has a shallow but massive dentary, relatively deep postdentary portion with two surangular foramina and somewhat elongated retroarticular process; on the lateral surface of the postacetabular process of the ilium there are two large depressions for muscle origins separated by a crestlike projection; the fibula is fused distally with the tibiotarsus and the coalesced astragalocalcaneum- Bagaraatan
represents the Tetanurae and displays some synapomorphies with the Avetheropoda, however, incompleteness of the skeleton of B. ostromi does not allow to determine its more precise affiliation. Bagaraatan was about 3'0-3.5 m
long, had a relatively small head and slender hind limbs. The presence of strongly developed hyposphenes in a long series of anterior caudals rendered its tail only slighily flexible proximally.

Key words: Dinosauria, Theropoda, Tetanurae, anatomy, habits, relationships.