SExperiments have been conducted to investigate the inhibitory effect of the catalytic reaction of methane and the formation of formaldehyde in the presence of NO. With precious metal catalysts, the presence of NO showed an inhibitory effect on the methane oxidation and caused the formation of formaldehyde. In the absence of oxygen, however, formaldehyde was not produced in the catalytic reaction of methane and NO. Maximum formation of formaldehyde was about 0.6 % of NO with the Pt and Rh series catalysts. N2O formation is similar to the formaldehyde formation from the catalytic oxidation of methane in the presence of NO.