Tomonaga Sanjūrō (朝永 三十郎, Tomonaga Sanjūrō, 1871–1951) was a Japanese academic and esteemed professor emeritus of medieval, renaissance, early modern, and Kantian philosophy at the University of Kyoto during the early 20th century.

His son, Shinichirō Tomonaga, is also renowned for receiving the 1965 Nobel Prize in Physics for the development of quantum electrodynamics.

After graduating from Nagasaki Ōmura Junior High School (now known as Nagasaki Prefectural Omura High School) and then First Higher School, he entered the Tokyo Imperial University.

He mainly lectured on Western philosophy and history of philosophy, and along with Nishida Kitarō and Tanabe Hajime, constituted the important intellectual Kyoto School movement of modern Japan.

Tomonaga was well known to be an unprolific writer but left a prestigious body of work and was mentor to many renowned Japanese philosophers, including Amano Teiyū, Obara Kuniyoshi, Yamauchi Tokuryū and Kosaka Masaaki.