The heterogeneous-catalytic ammoxidation of several mono- and disubstituted methylaromatics and heteroaromatics to their corresponding nitriles was studied. The reaction was carried out on an ammonium oxovanadium pyrophosphate ((NH4)(2)[(VO)(3)(P2O7)(2)]) generated during the catalytic process. The study shows that the catalytic activity and the nitrile selectivity depend mainly on the position and the electronic nature of the particular substituent due to a changed accessibility of the methyl group as well as a possible different electronic stabilization.