In this study, two types of coals were used as the reburning fuel to investigate the influence of the reburning zone stoichiometry SR(2), the primary NO level and the particle size on NO reduction. For both coals, the NO reduction can reach as high as 60-70% in the tested SR(2) range of 0.7-1.1. No optimum reburning zone stoichiometry was observed in this study. The NO reduction decreases monotonically with the decrease of reburning zone stoichiometry. The effect of particle size is only obvious for larger particle sizes. (C) 2009 Elsevier Ltd. All rights reserved.