Abstract: Percarboxylic acid solutions, in particular aqueous equilibrium percarboxylic acid solutions, with improved stability when in contact with stainless steel and also a process for the production thereof. The percarboxylic acid solutions contain a percarboxylic acid having 1 to 12 C atoms and one or two peroxycarboxyl groups and are characterized by a content of polyphosphoric acid of the formula H.sub.n+2 P.sub.n O.sub.3n+1, in which n is greater than or equal to 2.3, in a quantity of 0.2 to 10 wt. %. These solutions are distinguished in comparison with known solutions by reduced corrosive action and reduced decomposition in the presence of stainless steel. The solutions are obtainable by reacting a carboxylic acid with hydrogen peroxide in the presence of polyphosphoric acid of the above-stated type and quantity as the catalyst.