| Named By: | Masateru Shibata & Yoichi Azuma in 2015 |
| Time Period: | Early Cretaceous, 128 Ma |
| Location: | Japan, Fukui - Kitadani Formation |
| Size: | Uncertain due to lack of fossils with known elements probably representing juvenile individuals |
| Diet: | Herbivore |
| Fossil(s): | Holotype is a partial maxilla and teeth, with additional post cranial remains |
| Classification: | | Chordata | Reptilia | Dinosauria | Ornithischia | Ornithopoda | Hadrosauroidea | |
Koshisaurus is a monospecific genus of basal hadrosauroid from the Kitadani Formation in Japan. The discovery of the genus suggests that hadrosauroids had higher diversity along the eastern margin of Asia in the Early Cretaceous. "Koshi" means an old Japanese regional name including Fukui prefecture where fossils of the genus were discovered.