Abstract: The present invention relates to a process for preparing polyoxymethylene dimethyl ethers, comprising the following steps: reaction of formaldehyde and methylal (OME1) in a reactor R1 to obtain a product mixture, distillative separation of the product mixture in a distillation unit D1 into a top stream which contains OME1, OME2, formaldehyde, methanol and water, and a bottom stream which contains OME?3, mixing of the top stream drawn off from the distillation unit D1 with a methanol-containing stream, treatment of the mixture in a reactive distillation unit RD2 to form a top stream containing methylal and a water-containing bottom stream, introduction of the bottom stream drawn off from the distillation unit D1 into a distillation unit D3 and distillative separation of the polyoxymethylene dimethyl ethers.