| Named By: | Christian Erich Hermann von Meyer in 1860 |
| Time Period: | 99.6-89.3 Ma Late Cretaceous: Cenomanian - Turonian |
| Location: | Slovenia |
| Size: | Unavailable |
| Diet: | Carnivore |
| Fossil(s): | Partial remains |
| Classification: | | Chordata | Reptilia | Scleroglossa | |
Acteosaurus is an extinct genus of aquatic lizard that lived in the upper Cretaceous period. Its species, A. tommasinii and A. crassicostatus, were described in 1860 and 1993. Though A. crassicostatus is probably a junior synonym for Adriosaurus suessi, A. tommasinii was found to be similar to coniasaurs, mosasauroids, and a sister taxon to modern snakes in 2010.