Abstract: The absorption of carbon dioxide into aqueous ammonia solution using packed column was investigated. The volumetric overall mass transfer coefficients (KGav) for CO2 absorption into aqueous ammonia solutions were evaluated over ranges of main operating variables , that is, upto 16kPa partial pressure of CO2, 61-214 m3/(m2.h) gas flow rate, 0.75- 3.06 m3/(m2.h) liquid flow rate, 2%- 16% ammonia mass fraction, and 20- 50oC temperature. Experimental results show that the mass transfer process in CO2 absorption into aqueous ammonia solution is mainly controlled by the resistance in the liquid phase and the ammonia concentration has a great effect on the overall mass transfer coefficient.