A promising chemical absorption-biological reduction integrated process has been proposed. A major problem of the process is oxidation of the active absorbent, ferrous ethylenediaminetetraacetate (Fe(II)EDTA), to the ferric species, leading to a significant decrease in NO removal efficiency. Thus the biological reduction of Fe(III)EDTA is vitally important for the continuous NO removal. Oxygen, an oxidizing agent and biological inhibitor, is typically present in the flue gas. It can significantly retard the application of the integrated process. This study investigated the influence mechanism of oxygen on the regeneration of Fe(II)EDTA in order to provide insight on how to eliminate or decrease the oxygen influence. The experimental results revealed that the dissolved oxygen and Fe(III)EDTA simultaneously served as electron acceptor for the microorganism. The Fe(III)EDTA reduction activity were directly inhibited by the dissolved oxygen. When the bioreactor was supplied with 3% and 8% oxygen in the gas phase, the concentration of initial dissolved oxygen in the liquid phase was 0.28 and 0.68 mg l(-1). Correspondingly, the instinct Fe(III)EDTA reduction activity of the microorganism determined under anoxic condition in a rotation shaker decreased from 1.09 to 0.84 and 0.49 mM h(-1). The oxidation of Fe(II)EDTA with dissolved oxygen prevented more dissolved oxygen access to the microorganism and eased the inhibition of dissolved oxygen on the microorganisms.