Ogata Kōan (緒方 洪庵, August 13, 1810 - July 25, 1863) was a Japanese physician and rangaku scholar in late Edo period Japan, noted for establishing an academy which later developed into Osaka University. Many of his students subsequently played important roles in the Meiji restoration and the westernization of Japan in the Meiji period. His true name was Ogata Koreaki (緒方 惟章) or Ogata Akira (緒方 章); the name of Kōan was his courtesy name.
Ogata was born in 1810 to a family of low-ranking samurai of Ashimori Domain in Bitchu Province in what is now part of the city of Okayama. He moved to Osaka in 1825 with his father, and began studies in rangaku and medicine at a private academy run by Naka Tenyū from 1826. In1831, he relocated to Edo to continue his studies in western medicine, returning to Nagasaki in 1836 to study under the Dutch doctor Erdewin Johannes Niemann, despite the Tokugawa shogunate’s strict national isolation policy.
In 1838, Ogata returned to Osaka to establish his medical practice, and in the same year established the Tekijuku, an academy of rangaku studies, where he taught medicine, natural history, chemistry and physics for the next 24 years. Ogata used his small but precious collection of Dutch books, including a Dutch-Japanese dictionary and a Dutch encyclopedia, to teach his pupils to read scientific Dutch texts. He also wrote several books, including a treatise entitled “How to treat cholera”, which he compiled in haste from various European sources during the great cholera epidemic of 1858.