The effects of the hydrazine molar ratio, reaction temperature and addition of CO on the NOx reduction in flue gas containing 12% oxygen were determined in a pilot-scale flow reactor. The optimum reaction temperature and molar ratio for maximum NOx reduction were found to be about 873 K and 4.0, respectively. With CO, hydrazine provides a wider temperature window for effective NOx reduction. The proposed model predicts the reduction of NO reasonably well at high oxygen content.