A method for a gas phase catalytic oxidation reaction of a hydrocarbon, which comprises: subjecting an alkane having a carbon number ranging from 3 to 8 and/or an alkene having a carbon number ranging from 2 to 8 to a gas phase catalytic oxidation reaction to produce a vapor phase oxidation product in the presence of a mixed metal oxide catalyst, wherein the reacion is conducted in the presence of particles substantially inert to the reaction in an amount within a range of the same amount as the amount of catalyst to 99 wt. % in all particles.