A new approach for separately evaluating NO formation and NO reduction during coal combustion in a fluidized bed was investigated. Sixteen different coals were burned in a laboratory-scale bubbling fluidized bed combustor with three different char loadings, which were established by changing the inlet oxygen concentrations. NO conversion ratios (X-NO = the ratio of the mass of N atoms in the emitted NO to the mass of N atoms in the coal) were determined for the coals, and then "ultimate NO conversion ratios" (X-NO*) were obtained by extrapolation of the lines describing the dependence Of X-NO On O-2 consumption rate to an O-2 consumption rate of zero. The X-NO* values correspond to the values that would be obtained for a single coal particle burning in the absence of char particles. Using this technique, the contribution of char particles to NO reduction was evaluated. The X-NO* values depended on the N content and the O/N molar ratio of the coals. The bed temperature dependences of the sensitivity values (the slopes of the lines describing the dependence of X-NO on O-2 consumption rate), which include the contribution of NO reduction by char particles, differed substantially for the different coals. However, char loading had no clear effect on N2O emission. This result suggests that the reduction by the char particles involves the competitive reaction of NO and N2O, and the effect of the N2O reduction by burning char particles was less than NO reduction. Our results indicate the importance of taking into account the effects of NO reduction by char particles on overall NO, emissions during fluidized bed combustion of coal.