NO laser-induced fluorescence (LIF) imaging and quantitative fuel distribution measurements in aport-fuel-injected 4-valve stratified-charge single-cylinder SI engine have been conducted using a tunable KrF excimer laser. The correlations between NO formation region and fuel distribution have been investigated for the horizontal stratification realized by fuel (iso-octane) injection in only one intake port. The NO LIF intensity is proportional to the exhaust NOx emissions. The strong NO LIF intensity region in expansion stroke corresponds to the location of the region with equivalence ratio (ϕ) between 0.8 and 1.1 in the stratified fuel distributions at spark timing. The exhaust NOx concentration is proportional to the area of region with ϕ =0.8 - 1.1. The relationship between the local NO LIF intensity and the local equivalence ratio ( ϕ L ) in the stratified-charge operation shows that NO is mainly formed in the local region with ϕ L=0.8 - 1.1, but that the maximum formation occurs at ϕ L of -0.9. The local characteristic of NO formation in stratified-charge operations is in good agreement with the relationship between exhaust NOx emissions and equivalence ratio in homogeneous-charge operation. It is suggested that the local NO formation mechanism in stratified-charge operation is almost the same as that of homogeneous-charge operation.