This article aims to present the main difficulties in implementing the constitutional principle of due administrative legal process in sexual harassment investigations, especially regarding the selection and obtaining of evidence, as well as the production and evaluation of evidence. First, we analyze the contemporary contours of the principle of due administrative legal process (article 5°, LIV and LV of the Constitution of the Brazilian Federative Republic and articles 20, 21 and 22 - LINDB). Next, we present sexual harassment as an administrative disciplinary infraction. We deal with aspects related to conceptualization, typology and legal provisions. We also analyzed some jurisprudential precedents of the Federal Supreme Court and Superior Court of Justice. Finally, we point out the elements, production and valuation of evidence in the administrative disciplinary procedural investigation of conduct involving the practice of sexual harassment. At this point, we highlight how the nature of the infraction and the victim's condition of vulnerability interfere with the implementation of the guarantees of contradictory and full defense. We conclude that there is a precarious classification system regarding the administrative offense of sexual harassment. This dysfunction ends up having consequences for the development of substantial due process, including with regard to the institute of evidence collection, requiring the evolution of the legislator, in action to combat the practice of sexual harassment in the Public Administration and in terms of accountability.