Alexander Slidell MacKenzie (January 24, 1842 – June 13, 1867) was an officer in the United States Navy during the American Civil War.

His father was a well-known naval officer whose career had been surrounded in controversy; his uncles included William Alexander Duer, John Slidell, and Matthew C. Perry.

Naval Academy in 1855, he graduated in June 1859 and was assigned to the newly completed steam sloop of war Hartford.

Promoted to Lieutenant in August 1861, he was an officer of the gunboat Kineo during the conquest of the lower Mississippi River in 1862.

After the end of the war, he returned to the East Asia in Hartford, in which he served until June 13, 1867, when he was killed in action at Kenting, Taiwan, while leading a punitive expedition against the massacre of the entire crew of an American merchant bark Rover.