| Named By: | Wiffen in 1980 |
| Time Period: | Late Cretaceous |
| Location: | New Zealand, North Island |
| Size: | 12 meters long, skull 78 centimetres long |
| Diet: | Carnivore |
| Fossil(s): | Partial skull, vertebrae, ribs and metacarpals (from the flippers) |
| Classification: | | Chordata | Reptilia | Squamata | Mosasauridae | Mosasaurinae | |
| Also known as: | | Mosasaurus flemingi | Rikisaurus tehoensis | |
Moanasaurus (From Maori moana "sea" and Greek sauros "lizard"; meaning "Sea Lizard") was a genus of mosasaur from the Late Cretaceous period. Its fossil remains have been discovered in the North Island of New Zealand. Moanasaurus was a very large mosasaurine known originally from a disarticulated skull, vertebrae, ribs and paddle bones. It reached 12 m in length and the skull is 78 cm, which shows that Moanasaurus was one of the largest in the family of mosasaurinae.