A rigorous model for absorption of carbon dioxide into aqueous N-methyldiethanolamine ( MDEA) based on the assumption of reversible reactions and the simplified model with a pseudo-first order irreversible reaction hypothesis were employed to compare with experimental data. The experimental absorption rates were obtained from a characterized double stirred-cell absorber with a planar gas-liquid interface. It was demonstrated that the numerical solution of the rigorous model provides a better prediction for the absorption rate of carbon dioxide into aqueous MDEA solution than that of the simplified model. Only in the case of absorption experiments carried out at a low carbon dioxide partial pressure ( p < 20 kpa) and low amine concentration ( MDEA(total) < 1000 mol/m(3)), the assumption of pseudo-first order irreversible reaction is reasonable.