In this study, the gas phase volumetric overall mass transfer coefficients (K(G)a(e)) for CO2 absorption into aqueous ammonia solutions were measured to explore the mass transfer performance of a column packed with structured packing. The K(G)a(e) values were evaluated over ranges of main operating variables, that are, 1400-2300 m(3).m(-2).h(-1) gas flow rate, 20-39 m(3). m(-2).h(-1) liquid flow rate, up to 8 kPa partial pressure of CO2, and 0.27-0.72 kmol.m(-3) ammonia concentration. The results show that higher liquid loading and concentration of aqueous ammonia are beneficial to enhance the K(G)a(e) values. On the contrary, K(G)a(e) value decreases as the CO2 partial pressure increases. The results also show that gas loading has little influence on K(G)a(e). To allow the mass transfer data to be readily utilized, an empirical K(G)a(e) correlation for this system was developed. Finally, Simulations were made for the absorption of CO2 into aqueous ammonia solutions by using the currently developed computational mass transfer model along with the proposed correlation for K(G)a(e). The simulation results on the gas phase CO2 concentration are found to be in satisfactory agreement with the experimental measurements.