Alexander McDonald (April 10, 1832 – December 13, 1903) was a Republican politician who represented Arkansas in the United States Senate during the Reconstruction years from 1868 to 1871.

He served as a member of the state's constitutional convention; upon readmission to the Union he was elected by the Arkansas General Assembly to the Senate in 1868, with service for three years.

McDonald was later commissioned by U.S. President Chester A. Arthur to examine the conditions of portions of the Northern Pacific Railroad, a task he completed in 1885.

McDonald died in Norwood, a village in St. Lawrence County in northern New York State; his body was returned to Lock Haven for burial.

[1] McDonald's Little Rock home, the McDonald–Wait–Newton House, still stands and is listed on the National Register of Historic Places.