In the field of the CO2 absorption process using aqueous ammonia, the effects of regeneration pressure and temperature on CO2 absorption performances of the aqueous ammonia were investigated. The absorbents were prepared by dissolving ammonium carbonate solid in water to grant the resulted solution 0.5 CO2 loading (mol CO2/mol NH3) and various ammonia concentration (14, 20, 26 and 32 wt%). As-prepared absorbents were regenerated at high pressure and temperature (over 120 ℃ and 6 bar) before the absorption test. The absorption test was carried out by injecting the simulated gas that contains 12 vol% of CO2 into a bubbling reactor. The introduction of 26 wt% of the ammonia concentration for CO2 absorption test resulted in the higher absorption capacities than other experimental conditions. In particular, when the absorbents with 26 wt% of the ammonia were regenerated at 150 ℃ and 14 bar, the highest absorption capacity, 45 ml CO2/g, was obtained. According to the analysis of absorbents using acid-base titration, the ammonia loss during the regeneration of the absorbents with a fixed ammonia concentration decreased as the regeneration pressure increased, while it increased as the regeneration temperature increased. In the condition of fixed regeneration pressure and temperature, as expected, the ammonia loss increased as the ammonia concentration increased. The measured CO2 loadings and ammonia concentrations of absorbents were compared to the values calculated by Electrolyte NRTL model in Aspen Plus.