| Named By: | HenriinEmile Sauvage in 1873 |
| Time Period: | Middle-Late Jurassic, 160-155 Ma |
| Location: | England, France and Germany. Possibly further afield with possible fossils being located in Argentina and Mexico |
| Size: | Most complete specimen 6.39 meters long, isolated remains suggest that larger individuals reached 7-7.5 meters long |
| Diet: | unavailable |
| Fossil(s): | Many specimens, with material from several skulls. Only L.ferox represents an almost complete skeleton |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Pliosauroidea | Pliosauridae | |
| Also known as: | | Pliosaurus pachydeirus | Pliosaurus pachydirus | Thaumatosaurus mosquensis | |
Liopleurodon (meaning 'smooth-sided teeth') is a genus of large, carnivorous marine reptile belonging to the Pliosauroidea, a clade of short-necked plesiosaurs. The two species of Liopleurodon lived during the Callovian stage of the Middle Jurassic Period (c. 160 to 155 mya). It was the apex predator of the Middle to Late Jurassic seas that covered Europe. The largest species, L. ferox, is estimated to have grown up to 6.39 metres (21.0 ft) in length.
The name "Liopleurodon" (meaning "smooth-sided tooth") derives from Ancient Greek words: leios [leios], "smooth"; pleura, side or rib; and odon, tooth.