The invention relates to a method for preparing waste powder from generative production processes, by means of which three-dimensional objects are produced in layers from a powdery base material. The aim of the invention is to provide a method for the combined mechanical and material preparation of waste powder, wherein the waste powder is brought into such a structure that subsequently, by mixing with or even without new powder or mixtures of new and waste powders, a high-quality powdery material becomes available for generative production processes. This aim is achieved in that the waste powder is subjected to a mechanical treatment by reducing the waste powder to small pieces with a grinding mill.