Alessandro Achillini (20 October 1463 – 2 August 1512) was an Italian philosopher and physician.
He was born and died in Bologna, and is buried in the Church of Saint Martin there. He was celebrated as a lecturer both in medicine and in philosophy at Bologna and Padua, and was styled the second Aristotle.
His philosophical works were printed in one volume folio, at Venice, in 1508, and reprinted with considerable additions in 1545, 1551 and 1568.
He was also distinguished as an anatomist, among his writings being De humani corporis anatomia (Venice, 1516-1524), and Annotationes anatomicae (Bologna, 1520). He died at Bologna on the 2nd of August 1512. Amongst his notable discoveries, he is known as the first anatomist to describe the two tympanal bones of the ear, termed malleus and incus. In 1503 he showed that the tarsus (middle part of the foot) consists of seven bones, he rediscovered the fornix and the infundibulum of the brain.
His brother, Giovanni Filoteo Achillini, was the author of Il Viridario and other writings, verse and prose, and his grandnephew, Claudio Achillini, was a lawyer who achieved some notoriety as a versifier of the school of the Secentisti.