| Named By: | Henry Fairfield Osborn in 1905 |
| Time Period: | Late Cretaceous, 71-68 Ma |
| Location: | Canada. USA |
| Size: | Large individuals grew to over 10 meters long |
| Diet: | unavailable |
| Fossil(s): | Many individuals are known including a bone bed that contains the remains of twenty-two individuals in the same location |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Theropoda | Tyrannosauridae | Albertosaurinae | |
| Also known as: | | Deinodon sarcophagus | Albertosaurus arctunguis | Deinodon arctunguis | |
Albertosaurus (meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which the genus is named. Scientists disagree on the content of the genus, with some recognizing Gorgosaurus libratus as a second species.
As a tyrannosaurid, Albertosaurus was a bipedal predator with tiny, two-fingered hands and a massive head that had dozens of large, sharp teeth. It may have been at the top of the food chain in its local ecosystem. While Albertosaurus was very large for a theropod, it was much smaller than its larger and more famous relative Tyrannosaurus, growing to nine to ten metres long and weighing less than possibly 2 metric tons.
Since the first discovery in 1884, fossils of more than 30 individuals have been recovered, providing scientists with a more detailed knowledge of Albertosaurus anatomy than is available for most other tyrannosaurids. The discovery of 26 individuals at one site provides evidence of pack behaviour and allows studies of ontogeny and population biology, which are impossible with lesser-known dinosaurs.