Among Heidegger's works his Kant book, «Kant and the Problem of Metaphysics» (1929), takes a special place. Planned by Heidegger as one of the sections of the second part of «Being and Time», it was intended to show the importance of the problem of substantiation. In «Being and Time» Heidegger recognized the achievements of Kant, but at the same time he added that the penetration into the problem of temporality was beyond Kant's scope. Despite the fact that Kant has come very close to the problem of time, his investigations remained, according to Heidegger, within the framework of the traditional ontology. Taking into account the aforementioned features of the interpretation of Kant in «Being and Time», it looks astonishing, that in his Kant book of 1929 Heidegger intended to demonstrate the idea of the fundamental ontology of Dasein (which he developed in «Being and Time») with the example of the interpretation of «Critique of Pure Reason» as the foundation of metaphysics. Heidegger discovered «clarifcation of transcendence» in Kant's transcendental deduction of the categories and Kant's subjective deduction seemed to be a transcendental disclosure of the nature of subjectivity of the subject. However, it is important to note that in the book «Kant and the Problem of Metaphysics» it is a question not so much of the historical-philological interpretation of Kant, as of clarifying Heidegger's internal directional of the fundamental ontology by means of this interpretation. We will try to give a critical analysis of Heidegger's interpretation, taking into account that Heidegger's analysis of the Kantian heritage is the sample not of historical, but rather systematic and methodical debate. It is also one reason why this critical analysis can serve as a reliable support for a more accurate determination of the essence of the transcendental-phenomenological issues not only in Heidegger's works, but also in Kant's works.