The ammoxidation of propane to acrylonitrile was investigated over Ca-Bi molybdate oxide catalysts (CaxBi12-xMo12 oxide). The performance of the catalysts changed as a function of the oxide composition. The highest performance for the ammoxidation reaction was obtained around x = 6 in CaxBi12-xMo12 oxide catalyst. The maximum selectivity of acrylonitrile and conversion of propane were 63% and 15%, respectively. The maximum selectivity of acrylonitrile was obtained at a propane concentration of 50-70% and a O2/NH3 mole ratio of about 1.5 in the feed. It was found that the initial step of propane ammoxidation was the formation of a gas-phase propyl radical which would be subsequently converted to propene and acrylonitrile by a catalytic surface reaction.