Methacrolein is produced in a high yield by catalytically oxidizing isobutylene at a temperature of from 250.degree. to 500.degree. C. by using a catalyst represented by the formula:Mo.sub.a Co.sub.b Fe.sub.c Bi.sub.d Cs.sub.e X.sub.f Y.sub.g O.sub.hwherein X is either both vanadium and palladium, Y is at least one member selected from titanium, nickel, tin and zirconium, a=12, b=2-12, c=0.5-7, d=0.1-5, e=0.0005-0.5, f=0.01-2, g=0-5 and h is a positive number proportional to the number of oxygen atoms satisfying the average valency of the metal atoms stated in the formula, which catalyst has a high resistance to compression and abrasion and exhibits a high catalytic efficiency, mechanical strength and durability.