In this paper, absorption rates and capacities of CO₂ into aqueous mixture of 20.5wt%MDEA and HMDA(0.7, 3.5, 7.0 and 14.4wt%) were measured with gas circulating absorption equilibrium apparatus. To compare the relative fresh absorption rates of CO₂ into aqueous mixtures, absorption rates were measured at 50℃ with initial pressure, CO₂ mole fraction and gas circulating rate of 215kPa, 0.536 and 14.7 l/min respectively. And absorption capacities of CO₂ into aqueous mixtures were measured at 50℃ over a range of CO₂ partial pressure up to 80kPa. From this experiments, absorption kinetics of CO₂ into aqueous mixtures of MDEA and HMDA can be regarded as a pseudo-first order reversible reaction. In this system, apparent rate constants of mixture were increased from 25 to 292% than MDEA aqueous solution with increasing concentration of HMDA. Also, as increasing the concentration of HMDA, enhancement factor of CO₂ absorption capacities into aqueous mixtures were increased 13-238% than 20.5%MDEA aqueous solution at CO₂ partial pressure was 10kPa, and 4-108% increased at CO₂ partial pressure was 80kPa.