In this study, the possible use of HMDA (Hexamethylenediamine) as additive to enhance reaction between $CO_{2}$ and AMP (2-amino-2-methyl-1-propanol) which has higher absorption capacity than that of MEA (Monoethanolamine) was investigated. Also, the absorption capacity for $CO_{2}$ was compared with addition of HMDA, piperazine or MDEA (N-methyldiethanolamine) into $30;wt\%$ AMP at $40^{circ}C$ and $CO_{2}$ partial pressure ranging from 0.5 to 120 kPa. Apparent rate constant ($K_{app}$) and absorption capacity with the addition of $5∼20;wt\%$ HMDA into AMP increased $214.2∼276.3\%$ and $29.9∼91.7\%$ than those of AMP alone. As a result, when $5;wt\%$ HMDA added into AMP, the increasing rate of the absorption rate and the absorption capacity was found to be the highest. In addition, the absorption capacity increased $6.8\%,;9.8\%,;11.6\%$ with addition of MDEA, piperazine or HMDA respectively as compared to AMP alone at $CO_{2}$ partial pressure of 20 kPa. Consequently, HMDA as additive to improve absorption capacity of AMP was superior to other additives.