NO, reduction in reburning was experimentally and numerically investigated. In the experiments, NOx reduction in simulated exhaust gas was confirmed in a flow reactor system and the concentrations of intermediate products such as HCN and N2O were measured. By controlling the temperature and air ratio, NOx reducing reactions proceeded efficiently and a 40% reduction of NOx was observed when the initial NOx concentration was 100 ppm. The calculated results agreed with the experimental results very well. Reaction analysis showed that for the HCN reducing reactions in the burn-out zone, two temperature regions were important, and in these regions HCN was reduced to N2O and finally to N-2 even in an oxidizing atmosphere.