The oxidation of propene over mixed metal oxide catalysts based on cation substituted 2:1 bismuth molybdates (Bi2Mo1-xMexO6-y, Me = Ni (x = 0.0, 0.25)) and vanadates Bi2V1-xMexO5.5-y, Me = Mn(x = 0.25), and Mo(x = 0.0, 0.25 and 0.50) has been studied. At atmospheric pressure and temperatures of 350-550 degrees C, the Mo:V containing catalysts are more selective for acrolein production than either Bi2MoO6, Or Bi2VO5.5, but Ni :md Mn substitutions produced less selective catalysts. Small quantities of propylene oxide were observed, but attributed to gas-phase reactions which are partially quenched by all the catalysts investigated.