The amidation of ethylene with carbon monoxide and ammonia over supported Ru ammine complex ion catalysts under atmospheric pressure has been investigated. The catalytic activity was affected remarkably by Ru precursors, supports and pretreatment temperature. The catalyst with highest activity was obtained using Ru ammine complex salts and by the pretreatment at 180-200 degrees C. The selectivity to propiononitrile formation increased with the acidity of the supports, indicating that propionamide was formed on Ru entities and was successively dehydrated to propiononitrile on the acidic sites of the support.