In the last decade, the Landless Workers Movement (MST – Movimento dos Trabalhadores Rurais Sem-Terra, in Portuguese), which fights for land reform in Brazil, has radically changed its speech towards guidelines recommended by the agroecology. The aim of this study was to understand, from a theoretical-historical approach, the appropriation of the concept agroecology as a motto in the struggle for agrarian reform holded by the MST. Classic conceptions concerning the role of the peasantry in contemporary societies and attempts to make “theoretical bridges” with the speeches and the actions taken by the MST in its history, based in a documental analysis were conducted. The conclusion is that the defense of agroecology in the MST, based on a chayanovian speech, is on an upward curve, in contrast to the previous prevailing speech of collectivization and promotion of specialized large farm units inspired in the orthodox Marxism. It also points out that the agroecology, for the MST, goes far beyond the productive dimension, adding significant political questions.