A novel process has been developed to remove NO from flue gas using a basic solution of cobalt(II) diethylenetriamine. The cobalt(II) diethylenetriamine cation can not only bind NO but also activate oxygen in aqueous solution. When only cobalt(II) diethylenetriamine solution was used, NO was oxidized to soluble nitrite and nitrate by active oxygen. So O-2 in the gas phase is favorable for the absorption of NO as O-2 concentration is less than 6%. When hydrazine hydrate were added to the solution, NO was reduced to N-2 and almost no nitrate was found in the spent scrubbing liquor. O-2 reacted with active Co-II to inactive Co-III. Thus the removal efficiency of NO decreased with increasing O-2 concentration. The effects of liquid-to-gas ratio, cobalt(II) diethylenetriamine, (NH2)(2)center dot H2O concentration, and temperature on NO removal efficiency were also examined under aerobic condition. Results showed that cobalt(II) diethylenetriamine was a promising metal chelate for NO removal.