Modeling of solubility of acid gases in aqueous alkanolamine solutions is essential for design of an absorber for natural gas sweetening. In this work an apparatus similar to the device of Hayduk and Chen (1970), which was improved by Pahlavanzadeh and Motahhari (1997), for the measurement of gas solubility data by the synthetic method was used. The solubility of hydrogen sulfide in aqueous diisopropanolamine (DIPA) solution in mass concentration range of 30-40% for 101,325 Pa pressure and for temperature ranging from 313-343 K was reported. The obtained experimental solubility data of H2S in aqueous solutions of DIPA was used to predict the different interaction parameters of modified UNIQUAC-NRF model for calculating the activity coefficients. For nonideality of species in liquid phase, the UNIQUAC-NRF equation with ion-pair approach was applied. For long range interaction, the Pitzer-Debye-Huckel term was used.