This work aims to understand the origins and grounds of Supremo Tribunal Federal´s jurisdictional activism, that has been increased since Emenda Constitucional 45/2004. By relating it with the context of tensions between constitutionalism and democracy, it has been demonstrated that the consolidation of a democratic constitutionalism, which has taken to the global expansion of judicial power, has special features in Brazil, whose historiography process still reveals the existence of archaichs frameworks and the development of a symbolic constitutionalization. From this historical and theoretical analysis, it is showed how in Brazil, instead of taking place an activist movement of strengthening human rights by STF, the court itself extends its jurisdictional limits. It is acknowledged that the judicialization of social and political relations brought the judiciary to democratic scene, but it is discussed the legitimacy by replacing legislation for jurisdiction in the role of deciding moral issues from a society. Based in contemporary law theories, it is explained why there is a disbelief in the dignity of legislation and a preference for the judicial hegemony. There have been tested arguments in favor for the exclusiveness or the superiority of the Judiciary in constitutional issues. Furthermore, it is emphasized that democracy involves conflict and that law can offer a constitutional architecture of interaction between state departments without despising the politics´ role in building the reality.