| Named By: | Buffetaut & Ingavat in 1986 |
| Time Period: | Early Cretaceous, 130 Ma |
| Location: | Thailand |
| Size: | Unknown due to lack of remains |
| Diet: | Piscivore |
| Fossil(s): | Teeth |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Theropoda | Spinosauridae | |
Siamosaurus (meaning "Siamese lizard") is a genus of theropod dinosaur from Early Cretaceous Thailand. The size of the animal is unknown, but it may have reached a length of about 9.1 meters (30 ft). The type species, Siamosaurus suteethorni, was formally described by Buffetaut and Ingavat in 1986. There is very little information on this Cretaceous meat-eater, but it is known from teeth that closely resemble those of Spinosaurus; it may have eaten fish.