The thermal reaction of CH2O with NO2 has been investigated in the temperature range of 393–476 K by means of FTIR product analysis. Kinetic modeling of the measured CH2O, NO, CO, and CO2 concentration time profiles under varying reaction conditions gave rise to the rate constants for the following key reactions: (Formula Presented.) and (Formula Presented.) The error limits shown represent only the scatter (±1 σ) of the modeled values. In the modeling, the total rate constant for the CHO + NO2 reaction, k2 + k3, was not varied and the value reported by Gutman and co‐workers (ref. ) was used for the whole temperature range investigated here. The proposed reaction mechanism, employing these newly established rate constants, can quantitively account for nearly all measured product yields, including the [CO]/([CO] + [CO2]) ratios reported by earlier workers.