The kinetics of the partial oxidation of methane to formaldehyde (MPO) on the silica catalyst at 650 degrees C has been investigated using a flow recirculation batch reactor. The influence of methane and oxygen concentration on density of reduced sites of the catalyst under steady-state conditions has been evaluated by in situ oxygen uptake measurements (RTOC). The reaction order with respect to CH4 and O-2 is 0.9 and 0.2, respectively, while the density of reduced sites depends upon the square-root of the PCH4/PO2 ratio. A formal Langmuir-Hinshelwood (L-H) model, accounting for the dissociative activation of both CH4 and O-2 molecules, is adopted to describe the reaction kinetics of the MPO on silica catalyst.