Alexander McKenzie Buchanan (March 1, 1805 – August 26, 1868) was a Justice of the Louisiana Supreme Court from May 4, 1853 to May 6, 1862. Born in New York City, Buchanan read law in the office of Louisiana Supreme Court Justice Isaac Trimble Preston, gaining admission to the bar in 1826. Buchanan was a judge of the Fourth District Court before his ascension to the supreme court bench. He later served as the city attorney for New Orleans from 1867 to 1868.