Abstract: The kinetics of the absorption of NO in aqueous Co(en)_3~(2 ) solution was studied in a stirred reactor.Factors influencing the NO absorption rate,such as pH,oxygen concentration and(Co(en)_3~(2 )) concentration were investigated.The reaction between NO and Co(en)_3~(2 ) is found to be (1.8) order with respect to the NO concentration.The experimental results indicate that NO absorption rate increases with increasing pH and oxygen concentration.A rate equation for NO absorption in aqueous(Co(en)_3~(2 )) solution under the influences of mass transfer is established.