Disclosed is ammoxidation of C.sub.3 to C.sub.5 acyclic alkanes with NH.sub.3 and O.sub.2 using (1) a mole ratio of alkane:NH.sub.3 in the range from 2 to 16 and a mole ratio of alkane:O.sub.2 in the range 1 to 10 and (2) a mixture of particulate catalyst compositions, the first being especially effective to promote formation of an unsaturated nitrile and an olefin from the paraffin, and the second catalyst composition being especially effective to promote the conversion of the olefin to the unsaturated mononitrile. Catalyst compositions useful in the process are also disclosed.