Building organizational legitimacy, despite not yet being fully studied at the Brazilian context, is crucial for organizational longevity as are other strategic processes. Every interagency or interorganizational relationship may or may not lead to a status of legitimacy. Being recognized as legitimate or illegitimate traces the scenario for the survival or extinction of the organization under study, in this case, the Banco Nacional de Desenvolvimento Econômico e Social (BNDES). Amongst the various groups of stakeholders, the media may exert a significant power over the process of organizational (de)legitimation, once they act reinforcing existing ideas and interpretations, observing critically, highlighting or silencing specific discourses. At the same time, modern means of communication enable organizations to search for their own discursive space and try to make prevail their legitimation discourses. With this new possibility to contest discursive legitimation struggles, how do organizations behave? What are the strategies and discourses mobilized by organizations to win the discursive struggle and maintain the status of legitimate in the eyes of their audience? This dissertation uses Content Analysis as the research strategy and illustrates this organizational phenomenon under a qualitative interpretative approach, using the case of BNDES. Building on Vaara and colleagues works, the author researches and analyses a series of BNDES’s posts shared on it’s online social media fanpage, as a response to the delegitimation discourses published by traditional media. Six discursive strategies are identified, five of them had been previously described (normalization, rationalization, moralization, authorization, narrativization) and one (denial) is defined by the author. This work brings two theoretical contributions and a practical one: the first theoretical contribution is the novelty of approaching discursive legitimacy strategies through corporate communications on Facebook at a Brazilian context; the second is the identification and definition of a discursive strategy that has not been previously mapped by the Academy, the strategy of denial, and it’s interactions with other strategies. The third contribution and a practical one, is the magnification of the visibility of different actors with institutionalized interests about the legitimation discursive strategies.