Kinetics of the absorption of CO, into N-methyldiethanolamine (MDEA) + water were investigated at 30, 35, and 40 degrees C using a laboratory wetted wall column. Four systems of which 1.0, 1.5, 2.0, and 2.5 kmol m(-3) MDEA aqueous solutions were studied. The solubility and the diffusivity of N2O in amine systems were also studied. The N2O analogy was applied to estimate the solubility and the diffusivity of CO, in amine systems. Based on the pseudo-first order for the CO, absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. The second-order rate constant of CO, with MDEA was found to be as k(2,MDEA)/(m(3) kmol(-1)s(-1)) = 4.01 x 10(8) exp [ -5400/(T/K)]. The activation energy of the reaction of CO2 with MDEA is found to be 44.9 kJ mol(-1). Based on the comparision with liteature values, this model is satisfactory to represent CO2 absorption rates in MDEA + H2O for temperatures from 20 to 80 degrees C.