| Named By: | Hector in 1874 |
| Time Period: | Late Cretaceous, 77 Ma |
| Location: | New Zealand |
| Size: | Estimates have ranged from 13-20 meters long |
| Diet: | Piscivore/Carnivore |
| Fossil(s): | Many specimens are known |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Elasmosauridae | |
Mauisaurus ("Maui reptile") is a genus of plesiosaur that lived during the Late Cretaceous period around 77 million years ago in what is now New Zealand. It was the largest plesiosaur, and perhaps the largest marine reptile in New Zealand waters at the time. Numerous specimens have been attributed to this genus in the past, but a 2017 paper restricts Mauisaurus to the lectotype and declares it dubious.