In industrial gas processing, there is an increasing interest in gas absorption processes for the selective removal of H2S from gas streams with a high CO2/H2S radii. In this work, the selective absorption of H2S from a gas mixture with CO2 into N-methyldiethanolamine (MDEA) in a microporous tube-in-tube microchannel reactor (MTMCR) was studied. A high H2S removal efficiency of 99.85% could be achieved. The effects of various parameters such as MDEA concentration, liquid and gas flow rates, gas liquid ratio, absorbent temperature, mean micropore size and annular channel width of MTMCR on H2S removal efficiency and selectivity were explored. The results indicated that MDEA concentration, liquid and gas flow rates had significant influence on H2S removal efficiency and selectivity. With the increase of MDEA concentration and liquid flow rate, H2S removal efficiency increased while selectivity decreased. Increasing gas flow rate resulted in H2S removal efficiency decrease and the selectivity increase. The smaller micropore size and annular channel width led to higher H2S removal efficiency and lower selectivity. Furthermore, the micropore size had a bigger effect on H2S selective removal process than the annular channel width. The results obtained imply a great potential for MTMCR applied to the selective absorption of H2S. (C) 2015 Elsevier B.V. All rights reserved.