| Named By: | L. Makadi, M. W. Caldwell & A. Osi in 2012 |
| Time Period: | Late Cretaceous, 85.3-83.5 Ma |
| Location: | Hungary - Csehbanya Formation |
| Size: | Roughly about 6 meters long |
| Diet: | Carnivore/Piscivore |
| Fossil(s): | Almost complete skull and post cranial skeleton |
| Classification: | | Chordata | Reptilia | Squamata | Mosasauridae | Russellosaurinae | Tethysaurinae | |
Pannoniasaurus is an extinct genus of tethysaurine mosasauroid known from the Late Cretaceous Csehbanya Formation (Santonian stage) of Hungary. It contains a single species, Pannoniasaurus inexpectatus, dubbed "unexpected" because it was discovered in freshwater sediments, unlike other mosasaurs, which were marine predators. It was a medium sized mosasaur, reaching up to 6 m (20 ft).