Catalytic and physicochemical properties of V-Mo-Nb oxide catalysts (V0.3Mo1Nbx, where x = 0.05, 0.15, 0.22, and 0.27) have been studied in the ammoxidation of ethane. An increase in the Nb content in the samples is accompanied by an increase in the catalytic activity and selectivity to acetonitrile. It was established that a triple Mo5O14-like phase with a variable composition (V(0.23 +/- 0.3)Mo(1)Nbx, where. = 0.2 divided by 0.37) acts as an active component in the catalyst.