Alexander Duff, 3rd Earl Fife (18 April 1731 – 17 April 1811) was a Scottish nobleman.
Duff was the son of William Duff, 1st Earl Fife and younger brother of James Duff, 2nd Earl Fife.
He married. Mary Skene, daughter of George Skene.
He briefly held the title Earl Fife, and was succeeded by his eldest son. His younger son was General Hon. Alexander Duff.
He died at Duff House, Banff.