Nemegtomaia is estimated to have been around 2 m (7 ft) in length, and to have weighed 40 kg (85 lb), a size extrapolated from more completely known relatives. As an oviraptorosaur, it would have been feathered. Though Nemegtomaia does not possess any single feature that distinguishes it from other oviraptorids (autapomorphies), the combination of a crest, an enlarged first finger, and a high number of sacral vertebrae (eight), is unique to this taxon.
