The present invention relates to a process of oxidizing copper in a copper etching solution by using oxygen gas and/or air as an oxidizing agent, the process comprising the steps of: a) introducing the oxidizing agent into an acidic reduced copper etching solution comprising Cl− and Cu+, b) stirring the solution obtained in step a), and thereby allowing the reaction 2Cu++½O2 (aq)+2H+→2Cu2++H2O to occur, thereby producing an oxidized copper etching solution comprising less Cu+ than the reduced copper etching solution. An advantage of the present invention is that it provides an improved process at least in terms of the speed of the oxidation and the quality of the etching.