Born at Ichinoseki in Mutsu (Iwate), the son of Ōtsuki Genryō, a doctor of the Ichinoseki domain. Raised in a family of physicians, he took to learning from early childhood.
He became a pupil of Takebe Seian, a famous doctor of Ichinoseki, and began studying medicine. Seian was keenly interested in Dutch medicine and corresponded with Sugita Genpaku in Edo, and Gentaku was strongly influenced by him.
He went to Edo, entered Sugita Genpaku's school and also learned Dutch from Maeno Ryōtaku. The name Gentaku is said to combine one character each from his teachers Genpaku and Ryōtaku.
He went to Nagasaki and studied Dutch more deeply with the official Dutch interpreters. What he learned at the source served him greatly in his later research and teaching.
He was appointed a doctor of Sendai domain and came to live in Edo. There he opened the Shirandō, a school of Dutch learning (rangaku), teaching young people from all over the country. Fine pupils such as Udagawa Genshin and Inamura Sanpaku came out of it.
He published Rangaku Kaitei, an introduction to the Dutch language and Dutch learning. Written so that beginners could follow it, it led many people to take up rangaku.
On the day that fell on 1 January of the Western calendar, he gathered rangaku scholars at the Shirandō to celebrate the new year. This came to be called the Dutch New Year and was held almost every year afterward.
At the request of his teacher Sugita Genpaku, he completed the Revised Kaitai Shinsho, correcting the errors of the Kaitai Shinsho (it was published 28 years later). It was a great undertaking to pass on more accurate anatomical knowledge.
He interviewed Tsudayū and other castaways from Sendai who had returned from Russia, and compiled Kankai Ibun, an account with maps and illustrations. Their tale of a voyage around the world became a precious source on Russia and foreign lands.
At the Office for Translating Barbarian Books, set up under the shogunate's astronomy bureau, he worked on translating Dutch books. He also took part in Kōsei Shinpen, a translation of the Dutch edition of a French encyclopedia.
The Revised Kaitai Shinsho was finally published. That year Siebold, doctor of the Dutch trading post, visited Edo, and many rangaku scholars sought to learn from his new knowledge.
He died in Edo. The Shirandō had become the center for spreading Dutch learning across Japan, and his scholarship passed to his son Ōtsuki Genkan and his grandson Ōtsuki Fumihiko, who compiled the Japanese dictionary Genkai.
Maeno RyōtakuSugita GenpakuPhilipp Franz von SieboldHayashi ShiheiShiba Kokan
Uesugi YōzanDaikokuya KōdayūKitagawa UtamaroMogami TokunaiRyōkanMatsudaira SadanobuKatsushika HokusaiHanaoka Seishū
People of the Edo period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.