Nakaoka Shintarō (中岡 慎太郎, May 6, 1838 – December 12, 1867) was a samurai in Bakumatsu period Japan, and a close associate of Sakamoto Ryōma in the movement to overthrow the Tokugawa shogunate.

Later that year, as a member of the Kaientai formed by Sakamoto Ryōma, he worked to bring about the Satsuma-Chōshū Alliance and obtain the backing and support of Sanjō Sanetomi for the project.

In June, he began negotiations to further expand the new alliance to include Chōshū as well as Hiroshima Domain, but the issue was rendered moot when shōgun Tokugawa Yoshinobu formally returned governing power to the Emperor.

[1] Sakamoto died soon afterwards, but the critically injured Nakaoka lingered for two days, although never regaining enough consciousness to identify the attackers, though he did mention hearing Iyo dialect among the killers.

There is a large bronze statue of Nakaoka Shintarō at Murotomisaki lighthouse in Cape Muroto in his native Kochi Prefecture, and another (together with Sakamoto Ryōma) at Maruyama Park in Kyoto.