This paper proposes a new approach of applying an optimization technique to simultaneously determine a physical liquid-film mass transfer coefficient (k(L)(o)) and effective interfacial area (a(v)) from a pilot plant data. The mass transfer mechanism of the CO2-NaOH system was modeled using the two-film theory to represent the behaviors of packed absorbers. The model presents an overall absorption rate (R-v) as a function of k(L)(o) and a(v). The optimization algorithm used in this study follows a modified Levenberg-Marquardt method with a trust region approach. The R-v predictions from the model are in good agreement with the experimental data, with an average error of 6.5%.