The discussion with Islamic philosophy is one of the most important topics in the history of medieval philosophy. Furthermore, the criticism of the unity of intellect formulated by Christian medieval thinkers against Islamic interpreters of Aristotle, mostly against Averroes, is one of its most interesting elements. This element is well known and abundantly analyzed by medievalists. But a particular version of the theory of unity of intellect was formulated also by Avicenna who claimed that agent intellect, being the mover of the last celestial sphere, is one for all men. His conception, although not so popular in the Middle Ages as that of Averroes, was criticized by Giles of Rome, an eminent 13th century thinker, in his Commentary to Aristotle’s On the Soul. The reconstruction of Giles’s polemic against Av i cenna shows that Islamic thinkers, although criticized by Christian thinkers, were read carefully by them and treated seriously as interpreters of Aristotle’s thought.