Moanasaurus (From Māori 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 holotype CD43, a disarticulated skull, vertebrae, ribs and flipper bones.

The skull measures 78 cm (31 in) in length, which shows that Moanasaurus was one of the largest in the subfamily of Mosasaurinae.

[1] Researchers argue that some Antarctic Mosasaurus remains (including a "large, fragmentary skull") may be attributed to this genus.