The　radiation　reabsorption　effects　on　NOx　formation　and　flame　characteristics　in　CH4/Air　laminar　flames　were　numerically　investigated　by　using　full　chemistry　mechanism　and　detailed　transport　properties.　The　radiative　gases　were　treated　as　non-gray　gas　and　their　spectral　radiative　properties　were　evaluated　by　means　of　the　statistical　narrow-band　model.　The　radiative　heat　transfer　equation　was　solved　by　the　discrete　ordinate　method.　It　was　found　that　the　reabsorption　of　emitting　radiation　leads　to　substantially　wider　flame　thickness　and　higher　flame　temperature　than　those　calculated　by　using　the　optically　thin　model,　and　the　radiation　reabsorption　effect　on　the　＇radiation　extinction　limit＇　becomes　more　important.　The　results　show　that　the　level　of　NOx　is　predicted　to　be　highest　in　the　adiabatic　flames,　that　is,　flames　without　radiation　heat　loss,　and　that　the　level　of　NOx　is　predicted　to　be　lowest　in　the　flames　by　the　optically　thin　model.　In　the　flames　by　the　SNB　model,　the　predicted　amount　of　NOx　lies　between　these　two　levels.　The　calculated　results　also　show　that　the　radiation　reabsorption　effect　on　NOx　formation　grows　stronger　as　the　stretch　rate　decreases,　particularly　when　CO2,　a　strong　absorber,　is　added　to　the　unburned　gas　mixture.　In　this　study,　the　effectiveness　and　validity　of　the　optically　thin　radiation　model　for　calculating　NOx　formation　in　laminar　flames　was　also　investigated　in　comparison　with　the　SNB　model.　©　2010　by　ASME.