This work aims to understand the concentrated judicial control of constitutionality of any given positive discrimination law, based on the mechanism of preferred admissions for racial minorities in the public Universities. It`s been demonstrated that such control must follow the proportionality principle. That s because, on one side, the implementation of these measures involves a restriction on a fundamental right, that is, equality on its formal conception. Otherwise, it also involves the consideration of legislative facts and prognoses by the judiciary. Thus, this instance of control is only legitimate if carried out in line with the rules of rationalization imposed by the principle in question. It`s duty of the legislator to seek for the means capable of implementing the substantial conception of equality, as a way to put into practice the constitutional commandments, which may not be just ideological standards, but instruments for achieving the main objective of contemporary constitutionalism: the dignity of the human person. Therefore, it is necessary to rationalize the linkage between legislator and fundamental rights, especially in order to limit the margins of action. Indeed, the action of the judiciary branch is essential, restrained by the appointed limits, with the purpose of obtaining legitimacy as an important instrument of defense of a Democratic State. The suggested constitutionality control followed the principle of proportionality. Thus, legislative facts and prognoses were limited by the sub-principles of adequacy suitability of the employed means to achieve the aimed purposes and necessity inexistence of other harmlessly means, in attention to the idea of the smallest degree of intrusion as possible. In addition, the analysis of the stress between formal and material conceptions of equality was carried out considering the sub- principle ofproportionality in the strict sense, which operates a balancing of legal values in conflict.