The invention relates to a method for producing diaminodiphenyl alkanes, wherein an aromatic amine, which can be substituted or unsubstituted, is reacted with a C1-C3 aldehyde in the presence of a heterogeneous catalyst, said catalyst being a mesoporous acidic ion exchanger based on a divinylbenzene/styrene copolymer and the catalyst having acid centers in a concentration of 2 to 6 eq/kg measured according to DIN 54403 and the average pore diameter of the catalyst particles being 10 to 32 nm measured according to ASTM D 4222, and the content of polynuclear compounds in the reaction mixture being >10 and ˜15% by weight.