The emissions of nitrogen oxides during coal combustion contribute to acid rain and are a major environmental problem. In this investigation, the release of nitric oxide during the combustion of coal chars prepared from a wide range of coals in an entrained flow reactor was investigated over a range of combustion temperatures (823 - 1323K) using a thermogravimetric analyzer coupled with a mass spectrometer. The conversion of char nitrogen to NO (NO/char-N) was studied in relation to coal and char structural characterization parameters. The results show that higher levels of conversion of char-N to NO were observed for the high-rank coal chars at lower combustion temperatures, where the reaction is under chemical control. As the combustion temperature increased, there was a decrease in the NO/char-N conversion ratio. Chars with low surface areas and low reactivities tend to have higher levels of conversion of char-N to NO during combustion. The implications for the mechanism of NO reduction on the char surface and in the pores are discussed.