Ammoxidation of 2-, 3-, and 4-picolines to their nitrile compounds has been studied on an amorphous molybdenum phosphate (MoPO) catalyst with P/Mo=1.0. The overall catalytic results of this study reveal that the conversion is in the order 2-picoline>4-picoline>3-picoline, which can be rationalized neither by the steric effects nor by the thermodynamic point of view. However, the MoPO catalyst prepared here was found to be very effective for the ammoxidation reaction of picolines. Even at almost 100% conversion levels of all three picoline isomers, selectivities to their nitrile compounds on this MoPO catalyst were higher than 90% or so.