Minamoto no Mitsunaka (源 満仲?, April 29, 912? – October 6, 997), son of Minamoto no Tsunemoto, was a samurai and Court official of Japan's Heian period. Mitsunaka belonged to the Seiwa Genji branch of the Minamoto clan, which traced its ancestry to Emperor Seiwa. He loyally (if not selflessly) served several successive Fujiwara regents (sessho and kampaku) beginning with Fujiwara no Morotada. Mitsunaka allied himself with Morotada in 969, by implicating Minamoto no Takaakira—Morotada's major political rival—in a plot against the throne. It is not clear whether these accusations were true, but Takaakira was sent into exile, placing Mitsunaka firmly in Morotada's good graces. Later, Mitsunaka would assist Fujiwara no Kaneie in his plot to coerce Emperor Kazan into taking Buddhist vows and abdicating in favor of Fujiwara's seven-year-old grandson.
Mitsunaka's association with Fujiwara clan made him one of the richest and most powerful courtiers of his day. He served as the acting governor (kokushi) of ten provinces, most notably Settsu, which became the mainstay of his military and economic power. In addition, Mitsunaka inherited his father's title of Chinjufu-shogun, Commander-in-chief of the Defense of the North. The patron/client relationship between the Fujiwara and the Seiwa Genji continued for nearly two hundred years after Mitsunaka's death; indeed, the Seiwa Genji came to be known as the "teeth and claws" of the Fujiwara.
Mitsunaka married the daughter of Minamoto no Suguru, from the Saga Genji branch of the Minamoto. He was the father of three sons: Minamoto no Yorimitsu (who became the hero of a large body of folklore), Minamoto no Yorinobu, and Minamoto no Yorichika.