The medieval commentators of the Nicomachean Ethics paid special attention to the Aristotelian distinction between things that are just by nature and things that are just by law. This paper examines how three commentators from the first half of the 14th century understood this text: Radulfus Brito, Walter Burley and Geraldus Odonis. The interpretations of the first two was notoriously influenced by that of Aquinas, in spite of the Condemnation of 1277, since they understood Natural Justice in terms of Aquinas's theory of Natural Law. On his part, Odonis, who was the first Franciscan to write a commentary on the Ethics, is more original, as evidenced in (i) his idea that in all manifestations of Legal Justice there are always underlying natural elements; (ii) his concern to link Aristotle's teaching on Natural Justice with certain Platonic themes; and by (iii) his rather convincing analyses of the examples that Aristotle offers when addressing the possibility of change in both things that are just by nature and things that are just by law.