Baron Yamakawa Kenjirō (山川 健次郎, September 9, 1854 – June 26, 1931) was a Japanese samurai, politician, physicist, academic administrator, and author of several histories of the Boshin War.

After the Meiji Restoration, through the mediation of the Zen monk Kawai Zenjun, Yamakawa was placed in the care of Chōshū retainer Okudaira Kensuke.

Yamakawa was sent by the new Meiji government to study physics at Sheffield Scientific School, Yale University, where he was the first student from Japan to graduate.

He and his brother Yamakawa Hiroshi are known amongst historians of the late Edo period as authors of two monumental texts—Kenjirō's being "Aizu Boshin Senshi," which catalogues the actions of his home domain during the war.

Futaba, who fought in the Battle of Aizu during the Boshin War, later worked at the Tokyo Women's Normal School (東京女子高等師範学校, Tōkyō Joshi Kōtō Shihan Gakkō), the forerunner of Ochanomizu University.