The kinetics of oxidative gas-phase dehydrogenation of isobutyraldehyde over Cs2HPMo12O40 catalyst has been studied in a flow-through integral reactor at 523 K at atmospheric pressure. The catalytic reaction has been found to be accompanied by oxidation of isobutyraldehyde outside the catalyst bed. The rate of formation of methacrolein is satisfactorily described by the rate equation derived on presumption of change in the mean activation energy. The rate of the reaction in the homogeneous phase was described by empirical pseudo-first order equation.