The oxidation of propene over mixed metal oxide catalysts based on cation substituted 2:1 bismuth molybdates (Bi 2 Mo 1 - x Me x O 6 - y , Me = Ni (x = 0.0, 0.25)) and vanadates Bi 2 V 1 - x Me x O 5 . 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°C, the Mo:V containing catalysts are more selective for acrolein production than either Bi 2 MoO 6 , or Bi 2 VO 5 . 5 , but Ni and 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.