Oxide complex catalysts comprising Fe-Sb-Bi-O.sub.x promoted with a wide variety of different elements have been found to be especially useful in the ammoxidation of olefins to nitriles such as acrylonitrile and methacrylonitrile. Not only are the desired nitriles obtained with high yields when these catalysts are used, but also the production of unwanted liquid byproducts such as acrolein, acrylic acid and acetonitrile is significantly reduced.