Marshal Admiral Baron Ijūin Gorō (伊集院 五郎, 29 September 1852 – 13 January 1921) was a Meiji-period career officer in the Imperial Japanese Navy.

Promoted to rear admiral on 26 September 1899, Ijūin was a strong proponent of better relations between Japan and the United Kingdom, and worked to develop the Anglo-Japanese Alliance (1902) from behind the scenes.

He was on a diplomatic mission to the United Kingdom in 1902 with Major-General Fukushima Yasumasa, and was awarded an honorary Knight Commander of the Order of the Bath (KCB).

Ijūin was elevated to the title of danshaku (baron) in 1907 under the kazoku peerage system, became an admiral on 1 December 1910 and marshal-admiral on 26 May 1917, despite never having actually commanded a ship.

His son, the Admiral Ijūin Matsuji, also a career navy officer, perished in World War II during the Battle of Saipan in 1944.