The present invention relates to a method for preparing carboxylic acids comprising the step of contacting an aromatic hydrocarbon comprising at least one group including an α C-atom that is oxidizable to a carboxylic group in liquid phase with an oxygen containing gas in the presence of a heterogeneous catalyst with perovskite structure ABO3 with A being selected from at least one element of groups 1 to 3 of the Periodic Table, lanthanides or actinides, and B being selected from at least one element of the groups 4 to 15 of the periodic table or an oxygen-defective derivative of that catalyst having the formula ABO3−δ with 0