The lowering effects of reaction temperatures on both methane activation and C-1 oxygenates selectivity have been examined for the selective oxidation of methane in the gas-phase reaction of CH4-O-2-NO2 with CH2O addition (CH2Oadd) in a feed gas. Formaldehyde addition in the feed gas was effective to enhance methane activation. Reaction temperature was decreased ca. 50 K at 5% level of CH4 conversion by (CH2Oadd) to 1.1% level in the feed gas of CH4-O-2-NO2. This decrease was explained by the lowering effects of activation energy for hydrogen abstraction reaction from methane. Formaldehyde selectivity decreased at the same reaction temperature as the CH2Oadd concentration in the feed gas was increased. This decrease was explained by the increase of decomposition reaction between produced CH2O and OH which was produced through CH2O related reactions. The enhancement of CH3OH selectivity by the addition of CH2O in a lower temperature region was observed, It was explained by newly appeared CH3OH formation route, which was derived from the CH2Oadd in the feed gas.