In order to study the effect of flue gas recirculation (FGR) by primary air mixed with FGR or nitrogen on NOx emissions in a fixed total primary air flow rate, the bed temperature, stoichiometric oxygen ratio in the combustion chamber, and excess oxygen ratio were investigated in a pilot-scale vortexing fluidized-bed combustor (VFBC). As a result, the NOx emissions could effectively be decreased with FGR in the VFBC. The lower NOx emissions were attributed to the fact that the FGR allows NOx to enter the reactor again with the chance of being reduced and that the FGR contains more CO2 to suppress NOx formation or promote NOx reduction through its conversion to CO by reaction with char.