Ii Naosuke (井伊 直弼 Ii Naosuke, 1815 - March 3, 1860) was Tairo of Japan from April 23, 1858 until his death. He is most famous for signing the Harris Treaty with the United States, granting ports and extraterritoriality to American merchants and seamen.

He was born as the fourteenth son of Ii Naonaka , daimyo of Hikone (Omi Province). Because of his low rank within the family, he was not expected to take up any position of importance, so he moved into a Buddhist monastery and subsisted off of a meager stipend during the early years of his life.

However, Ii's older brothers gradually died or were adopted into other families, placing him at the fore to inherit his father's domain. In 1850, Ii's last remaining elder brother died, so he inherited the lordship of Hikone.

Ii was active in the reform of the bakuhan taisei system, as well as in the defense of Tokyo Bay during the arrival of Matthew C. Perry.

In 1858, when Shogun Tokugawa Iesada became ill, the daimyo argued over who should run Japan in the interim. Ii won the tairo election against Hitotsubashi Keiki, who was supported by the tozama domains of the west.

Ii was in favor of opening Japan to the West, which caused friction with sonno joi rebels supporting the expulsion of "barbarians" from the country. He attempted to halt the opposition with the Ansei Purge, which arrested or executed more than a hundred isolationist leaders.

He was murdered in the middle of the night by a band of seventeen ronin near Sakurada Gate, Edo Castle.