Abstract: For production of acrolein by gas-phase catalytic oxidation of propylene with molecular oxygen, there is used a catalyst containing molybdenum, bismuth, cobalt, nickel, iron, tin, silicon, and a particular borate in a prescribed proportion. Sodium or manganese is employed for formation of the desired borate. For preparation of the catalyst, the borate of each of the metals is preferably supplied in the combined form of a sodium or manganese salt of various boric acids, such as borax, although it may be supplied separately as a boric acid and a decomposable compound of each metal.