| Named By: | John Bell Hatcher in 1903 |
| Time Period: | Late Jurassic, 155-152 Ma |
| Location: | USA, including Colorado and Wyoming - Morrison Formation |
| Size: | Known to be up to 14.8 meters long |
| Diet: | Herbivore |
| Fossil(s): | Few individuals represented by partial post cranial remains |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropodomorpha | Sauropoda | Diplodocoidea | Haplocanthosauridae | |
| Also known as: | | Haplocanthus | Morosaurus agilis | |
Haplocanthosaurus (meaning "simple spined lizard") is a genus of sauropod dinosaur. Two species, H. delfsi and H. priscus, are known from incomplete fossil skeletons. It lived during the late Jurassic period (Kimmeridgian stage), 155 to 152 million years ago. The type species is H. priscus, and the referred species H. delfsi was discovered by a young college student named Edwin Delfs in Colorado, USA. Haplocanthosaurus specimens have been found in the very lowest layer of the Morrison Formation, along with Hesperosaurus, Brontosaurus yahnahpin, and Allosaurus jimmadensi.