Alvarezsaurus (/ˌælvərɛzˈsɔːrəs/; "Alvarez's lizard") is a genus of alvarezsaurid dinosaur from the Late Cretaceous, living in Argentina approximately 86 - 83 million years ago.

[1][2] It was found in the Bajo de la Carpa Formation and was named by paleontologist José Bonaparte in 1991 after the historian Don Gregorio Alvarez.

[4] Spinal processes were entirely absent or poorly developed, and each caudal vertebra supported short prezygapophyses.

The scapula was visibly curved and proportionally smaller than those of other alvarezsaurids, and unlike its relatives Alvarezsaurus did not have a fused astragalus and calcaneum.

[citation needed] Alvarezsaurus is considered basal to better-known members of its family, such as Mononykus and Shuvuuia.