Acrolein or methacrolein is produced in a high percent of yield by a catalytic oxidation of propylene or isobutylene in the presence of a catalyst of the empirical formula:Mo.sub.10 Co.sub.0.about.10 Ni.sub.0.about.10 Fe.sub.0.1.about.5 Bi.sub.0.001.about.3 Al.sub.0.05.about.10 Ti.sub.1.about.15 A.sub.0.about.4 O.sub.33.2.about.99wherein A denotes at least one alkali metal atom and the sum of the numbers of cobalt atoms and the nickel atoms is 1 to 10 per 10 atoms of molybdenum, which catalyst has an excellent crushing strength and exhibits a high catalyst activity.