Experiments were conducted in a drop-tube furnace (DTF) to investigate NO emission characteristics of low-rank bituminous coal burning in the primary combustion zone. The combustion tests were performed under high-stoichiometric-ratio (SR) combustion conditions (SR g 1) and low-SR combustion conditions (SR<1). Along the length of the furnace, concentrations of flue gas species, such as NO, HCN, NH 3 , CH 4 , CO, CO 2 , and O 2 , were carefully measured during pyrolysis and different SR combustion conditions. The results for high-SR combustion conditions show that high concentrations of O 2 favor the conversion of volatile N and char N into NO, with extensive NO formation taking place in the initial stages of combustion. Reducing species, such as CH 4 , C 2 H 6 , and NH 3 , in volatile matter were mostly oxidized and generated little effect on NO elimination. Results from low-SR combustion conditions show that there is insufficient O 2 for oxidization of combustibles, allowing more hydrocarbons to react with NO. For the coal tested in these experiments, the conversion ratio of fuel N to NO, R fuel N , yielded the lowest minimum values around SR = 0.9 among all such ratios because of a larger fraction of fuel N being decomposed from coal particles through pyrolysis, as well as char oxidization being reduced to N 2 . For lower SR conditions, the total fixed nitrogen (TFN), which includes NO, NH 3 , and HCN, can be reduced to N 2 by homogeneous reactions, so that the remaining N in char becomes the major contributor of NO emissions in the burnout zone.