Oliver Perry Hay (May 22, 1846 – November 2, 1930) was an American herpetologist, ichthyologist, and paleontologist.

In 1870, Hay graduated with a bachelor of arts from Eureka College in Illinois.

From 1894 to 1895, he worked at the Field Museum of Natural History as assistant curator of zoology, where despite his specialty in ichthyology, he worked in all nonornithological fields of zoology.

In 1912, Hay was appointed as a research associate at the Carnegie Institution for Science, and was given office space at the United States National Museum.

The catalogs that he constructed were a great aid in recording existing knowledge and became standard references.