| Named By: | Gross in 1950 |
| Time Period: | Middle Devonian-Late Devonian |
| Location: | Germany and Western Australia |
| Size: | About 9 centimetres long |
| Diet: | Carnivore |
| Fossil(s): | Specimens preserved flat on slabs |
| Classification: | | Chordata | Actinopterygii | Palaeonisciformes | |
Moythomasia is an extinct genus of early ray-finned fish from the Devonian period of Europe and Australia.
Moythomasia was a small freshwater fish, 9 centimetres (3.5 in) long. It had relatively large eyes, presumably to find prey in murky water. Its body was covered in specialized ganoid scales; the upper side of each scale sported a small pin that perfectly fit into the hollow lower side of the next scale. This allowed the fish to be both armored and flexible.