| Named By: | Jose F. Bonaparte in 1991 |
| Time Period: | Late Cretaceous, 86-83 Ma |
| Location: | Argentina - Bajo de la Carpa Formation |
| Size: | Estimated about 2 meters long |
| Diet: | Insectivore |
| Fossil(s): | Partial remains |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Theropoda | Alvarezsauroidea | Alvarezsauridae | |
| Also known as: | | Achillesaurus | |
Alvarezsaurus ("Alvarez's lizard") is a genus of small alvarezsaurid dinosaur from the Late Cretaceous period of Argentina, approximately 86 - 83 million years ago. Estimates suggest that it measured about 2 meters (6.5 ft) in length and weighed approximately 20 kg (45 lbs). Gregory S. Paul estimated in 2010 its weight at 3 kg and length at 1 m. It was found in the Bajo de la Carpa Formation and was named by paleontologist Jose Bonaparte in 1991 after the historian Don Gregorio Alvarez. The type species is A. calvoi.