The purpose of this work is to show how the proportionality concept has been approached in mathematics textbooks adopted in Brazil during the 20th Century. To consider the proportionality concept under the perspective of its historical development and under the point of view of the didactical phenomenology contributed to the understanding of the textbooks, because it showed that this concept is placed in the confluence of many others and, thus also brought explanations on its importance for the teaching of mathematics. We analized elementary school textbooks which were important and widely used. Based on these analyses it was possible to identify changes in the treatment of the proportionality concept, considering the theoretic, algorithmic and didactic aspects of the approaches, and the current presentations of the proportionality concept is compared to former approaches.