Disclosed is a method for ammoxidizing C.sub.3 to C.sub.5 mono-olefins to .alpha.,.beta.-mono-unsaturated acyclic nitriles having 3 to 5 carbon atoms and HCN by introducing such mono-olefins molecular oxygen and ammonia into a reaction zone into vapor phase contact with a solid ammoxidation catalyst, wherein the mol ratio of introduced molecular oxygen and ammonia to said introduced mono-olefin is at least 1.5 and 1.0, respectively, wherein said catalyst contains the elements and proportions indicated by the empirical formula:V1Sb.sub.a M.sub.m N.sub.n O.sub.xwherea=0.5 to 2M=one or more of: Sn, Ti, Fe, and Gam=0.05 to 3, usually at least 0.1 and at most 1N=one or more of: W, Bi, Mo, Li, Mg, P, Zn, Mn, Te, Ge, Nb, Zr, Cr, Al, Cu, Ce, Bn=0.0 to 0.5,and wherein the preparation of the catalyst includes contacting in an aqueous dispersion a vanadium compound and an antimony compound while said vanadium is in solution.