This paper analyzes the uses of epistolary genre in nine un-published letters written by Argentine author Eduarda Mansilla and addressed to two different presidents of her country: three to Julio Roca (dated from 1880 to 1881) and six to Juárez Celman (dated from 1887 to 1890). Some explanations about epistolary genre (mainly by Barrenechea, Violi, Guillén, Pagés-Rangel, and Castillo) are taken into account to theoretically frame the analysis. Ideas about the link between gender and letters proposed by Nancy Armstrong are considered as well, together with the historical contextualization of the culture of Rio de la Plata in Nineteenth-Century, as drawn by Sáenz Quesada, Barrancos, and Cicerchia. We propose that Mansilla (in opposition to other Nineteenth-Century female writers but following a tradition of powerful women in her family), has used this genre to get some moderate benefits for her family. These letters, also, contribute to understand Mansilla´s literature in the sense that they are built on three characteristics also present in her public literary prose: her critical gaze toward Argentina, her deep knowledge of Europe and her sense of class (or, in other words, her perception of Argentina as a land that owes her certain natural privileges?).