Alvarezsaurus is a small dinosaur from the Upper Cretaceous of Argentina, about 86–83 million years ago. It measured about two meters in length and weighed 20 kilograms.
It was named by paleontologist Jose Bonaparte in 1991. It walked on two legs, had a long tail, and its leg structure suggests that it was a fast runner. It may have eaten insects. It was more basal than other, better-known, members of its family, such as Mononykus and Shuvuuia.