The invention relates to a process for the preparation of polycarboxylic acids and derivatives thereof, the polycarboxylic acids prepared containing at least three carboxyl groups, comprising the steps(A) introducing one or more organic compounds, which contain nonaromatic carbon-carbon (C--C) double bonds, into water,(B) ozonolysis of the organic compounds in water by passing in an ozone-containing carrier gas,(C) addition of an aqueous hydrogen peroxide solution, to oxidatively work up the ozonolysis products produced in step (B), which comprises, in step (A), introducing the organic compound(s) into water having a pH of 7 or less than 7 and, in step (C), adding hydrogen peroxide in water without adding an organic solvent.