| Named By: | John Wells Foster in 1838 |
| Time Period: | Late Pliocene - Late Pleistocene, 3-0.011 Ma |
| Location: | Canada - Ontario, Yukon. USA - Alabama, Florida, Georgia, Illinois, Iowa, Kansas, Michigan, Nebraska, New Jersey, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia |
| Size: | Largest individuals up to 2.2 meters long, not including the tail |
| Diet: | Herbivore |
| Fossil(s): | Multiple individuals |
| Classification: | | Chordata | Mammalia | Rodentia | Castoridae | Castoroidinae | Castoroidini | |
| Also known as: | | Castoroides nebrascensis | Burosor efforsorius | |
Castoroides, or giant beaver, is an extinct genus of enormous beavers that lived in North America during the Pleistocene. C. leiseyorum and its northern sister species Castoroides ohioensis, were the largest beavers to ever exist.