This paper deals with ethics according to a psychoanalytical perspective and aims at distinguishing the ethics of Psychoanalysis from Kant's morals. The problematic consists in circumscribing the dimension of desire, in opposition to universal imperatives that try to eliminate the personal determinations in the field of moral action. The procedure observes Jacques Lacan's approach, whose particular interpretation of Kant's morals, articulated to Sade's anti-morals, unveils common points between these two diametrically opposing conceptions in the sense that the latter would unveil the hidden truth of the former. It is verified that Kant's categorical imperative and Sade's anti-morals share formal aspects of the law, aspects which the Psychoanalysis consideration about ethics discloses when isolating the inherent jouissance to the moral action and the subjacent imperative to the libertine action. It is concluded then that Psychoanalysis ethics acknowledges both a dimension of the non-eliminable jouissance in the subject as well as the alterity that conditions the desire from the point of view of the unconscious, identifying law and desire.