This article analyzes the process of nationalization of secondary education in Argentina in the second half of the nineteenth century considering the case of the province of Buenos Aires. First, it describes the organization of the preparatory education which depended on the University of the State of Buenos Aires, before the organization of the Nation. Then, it focuses on the tensions around degrees validation during the creation of the national schools, modifications in the curriculum at the University Department of Preparatory Studies and how the private sector was regulated. Finally, it analyzes the creation of the Provincial Secondary School of La Plata and its nationalization. It concludes that the Federal State by the 1880s, and through the national secondary schools, managed to become the only secondary public offer and to regulate the private sector. Thus, secondary education was established as a national issue. Received: 13/04/2013 / Accepted: 07/08/2013 How to reference this article Schoo, S. (2014). Conflictos y acuerdos en el proceso de nacionalización de la educación secundaria en Argentina en el siglo XIX. El caso de la provincia de Buenos Aires. Espacio, Tiempo y Educación, 1(2), pp. 113-131. doi: http://dx.doi.org/10.14516/ete.2014.001.002.005