| Named By: | T. Wegner in 1914 |
| Time Period: | Berriasian |
| Location: | Germany - Buckeberg Formation |
| Size: | Holotype individual about 3.25 meters long |
| Diet: | Piscivore |
| Fossil(s): | Skull and almost complete specimen |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | |
Brancasaurus (meaning "Branca's lizard") is a genus of plesiosaur which lived in a freshwater lake in the Early Cretaceous of what is now North Rhine-Westphalia, Germany. With a long neck possessing vertebrae bearing distinctively-shaped "shark fin"-shaped neural spines, and a relatively small and pointed head, Brancasaurus is superficially similar to Elasmosaurus, albeit smaller in size at 3.26 metres (10.7 ft) in length.
The type species of this genus is Brancasaurus brancai, first named by Theodor Wegner in 1914 in honor of German paleontologist Wilhelm von Branca. Another plesiosaur named from the same region, Gronausaurus wegneri, most likely represents a synonym of this genus. While traditionally considered as a basal member of the Elasmosauridae, Brancasaurus has more recently been recovered as a member, or close relative, of the Leptocleididae, a group containing many other freshwater plesiosaurs.