The equilibrium solubility of H2S, CO2, and their mixed gas in a solution of N-methyldiethanolamine (MDEA) mixed with ethylene glycol (EG) has been measured at temperatures from 25 to 90 degreesC, partial pressures of H2S from 0.34 to 38.8 kPa, and partial pressures of CO2 from 1.92 to 95.4 kPa. The solubility of either CO2 or H2S in mixed MDEA solutions was compared with that in 30 wt % MDEA aqueous solutions. The result shows that the CO2 solubility in MDEA mixed with EG is much lower than its solubility in aqueous MDEA solutions because the reaction between MDEA and CO2 would be limited by a very low water content. However, the H2S solubility is only somewhat lower than that in aqueous MDEA solutions only considering its lower solubility in EG than in water. This result indicated that the selectivity of H2S against CO2 is improved. A simplified model was proposed to correlate the experimental data and the average deviation for solubility of H2S and CO2 is 4.59% and 6.19%, respectively. The enthalpy changes of solving of CO2 and H2S in solutions of MDEA mixed with EG depend on the loading of acid gases, and it is lower than that of solving in aqueous MDEA solutions. This phenomenon may be explained by the fact that the degree of solvation in an organic solvent is less than that in water.