Nemegtosaurus (meaning 'Nemegt lizard') was a sauropod dinosaur from Late Cretaceous Period of what is now Mongolia. It was named after the Nemegt Basin in the Gobi Desert, where the remains — a single skull — were found. It may have had a long, sloping head and, like most sauropods, had peg-shaped teeth.
The type species, Nemegtosaurus mongoliensis, was first described by Nowinski in 1971. A second species, N. pachi, was described by Dong in 1977, but is a nomen dubium.
Comparisons between the scleral rings of Nemegtosaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day at short intervals.