| Named By: | Othniel Charles Marsh in 1888 |
| Time Period: | Oligocene-Miocene |
| Location: | Pacific coastlines of North America, Russia and Japan |
| Size: | 1.8 meters long |
| Diet: | Herbivore |
| Fossil(s): | Multiple specimens |
| Classification: | | Chordata | Mammalia | Paenungulata | Desmostylia | Desmostylidae | |
| Also known as: | | Desmostylella | Vanderhoofius coalingensis | |
Desmostylus is an extinct genus of herbivorous mammal of the family Desmostylidae living from the Chattian stage of the Late Oligocene subepoch through the Late Miocene subepoch (28.4 mya--7.250 Mya) and in existence for approximately 21.2 million years.