A series of MoV 0.3 Te 0.25 Sb x (x=0–0.6) mixed oxide catalysts have been hydrothermally prepared and tested for the partial oxidation of isobutane. XRD results show that a new crystalline phase TeMO (M=Mo, V and Sb) structurally similar to the structure of Te 3 Mo 2 V 2 O 17 is formed by incorporation of Sb ions into the Mo–V–Te-based system. Catalytic tests show that very high selectivity to methacrolein (48.6%) can be obtained at 15.1% of isobutane conversion at 390°C over a hydrothermally synthesized MoV 0.3 Te 0.23 Sb 0.5 catalyst.