In modern philosophy, the status of the concept of the thing-in-itself and the history of its origin and transformation are being conceptualized. This article examines the conceptual shift that happened to the notion of the thing-in-itself in XIX century philosophy, because this notion still remains important in the context of the possibility of having knowledge about reality and the status of reality itself. The rethinking of the thing-in-itself in the philosophy of Schopenhauer, Nietzsche and neo-Kantianism of the Marburg school (Cohen, Cassirer, Natorp) is considered. A comparative analysis of the works of all these authors allows us to say that the primary orientation of all these authors is to the specific elimination of the concept of the thing-in-itself. The thing-in-itself outside Kantian philosophy went through changes connected with an attempt to get rid of it or to define it in a non-contradictory (because the transcendent form of thing-in-itself gives us a contradiction) way for transcendental philosophy.