Satō Issai (佐藤一斎, November 14, 1772 - October 19, 1859) was a Confucian scholar in late Edo to Bakumatsu period Japan.
Satō was assigned to accompany him as his valet, and also entered the Shōheizaka Gakumonjo school for Confucian studies.
He was a quick learner, and by 1805 had risen to the position of head of the school and was recognized as a Confucian master with many of his own disciples.
Satō taught the orthodox Cheng–Zhu school of Neo-Confucianism which was favored by the shogunate, but he was also instrumental in the spread of Yangmingism, which became an influence on the incipient Sonnō jōi anti-foreigner movement in 19th-century Japan and was an integral part of the ideologies behind the Meiji Restoration.
Over time, Satō had 3,000 students, including Sakuma Shōzan, Watanabe Kazan, Yokoi Shōnan, Nakamura Masanao and many other figures who were highly influential in Bakumatsu-period Japan.