| Named By: | A. G. Sennikov & M. S. Arkhangelsky in 2010 |
| Time Period: | Late Triassic, 210 Ma |
| Location: | Russia, Franz Josef Land - Wilczek Formation |
| Size: | Uncertain |
| Diet: | Piscivore |
| Fossil(s): | Partial skeleton |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Elasmosauridae | |
Alexeyisaurus is an extinct genus of elasmosaurid plesiosaur known from the upper Triassic (lower-middle Norian age) of Wilczek Formation, Wilczek Land, of Franz Josef Land, Russia. It was first named by A. G. Sennikov and M. S. Arkhangelsky in 2010 and the type species is Alexeyisaurus karnoushenkoi.