Partial oxidation of methanol to formaldehyde by using a mixture of ferric and molybdenum oxides as the reaction catalyst at 280-330degreesC has been studied in a continuous fluidized bed reactor. The reactor was a cylindrical tube of 20 turn in i.d. and 36 mm in o.d. placed vertically and connected to a truncated coneshaped cyclone separator. The catalyst was prepared by the precipitation method using aqueous solutions of ammonium heptamolybdate and ferric nitrate. The effect of certain parameters, such as temperature, superficial gas velocity and feed flow rates, on the extent of oxidation reaction has been investigated. The maximum size of the catalyst particles was 990 mum, therefore, neither external nor internal diffusion was expected to be effective in the process. The experimental data were correlated with three classes of hydrodynamic models presented for fluidized systems. The best correlation was obtained with compartment type models.