Acrolein is produced by oxidizing propylene, in the gaseous phase, with a mixt. of O2 and steam using a catalytic system consisting of oxygen compounds of Mo, Bi, Fe and Co, in the atomic proportions of Mo, 40-67.6%; Bi, 1.9-21.7%; Fe, 1.6-6.5%; and Co, 21.0-48.1%. The reaction is carried out at a concn. of 1-10 mole % of propylene, 20-90 mole % of air, and 5-50 mole % of steam, and at a temp. between 300 degrees and 450 degrees C, pref. 330-420 degrees C, with a contact time of 0.5-15 sec. The catalyst has a low cost and has a high selectivity and activity.