The partial air oxidation of methanol to formaldehyde was studied in vapour phase over MoO3, Sb2O4 and their mixed oxides using an integral fixed bed flow reactor at atmospheric pressure and temperatures between 623 and 723 K. The effect of operational parameters on the conversion of methanol and selectivity of the catalyst were investigated. The optimum catalyst composition had a Sb2O4/MoO3 ratio of 2. The maximum yield of formaldehyde nearly 100%, with a 100% selectivity and about 100% conversion was obtained at 698 K with a W/F of 27.5 and 6% methanol in air. The rate expression r = k(1)P(M)/1 + 0.5k(1)P(M) / k(2)P(O2) based on a steady state and involving a two stage irreversible oxidation process correlated the data well.