A novel bimetallic MIL-101(Cr, Mg) was successfully synthesized for the first time by doping Mg during the solvothermal synthesis of MIL-101(Cr), and then characterized. The doped magnesium was homogeneously dispersed in the crystals of MIL-101(Cr, Mg). The magnesium ions had successfully coordinated with the carboxylic group in BDC through Mg-O. The synthesized MIL-101(Cr, Mg) remained excellent moisture-stability after exposed to humid air with 90% relative humidity for 30 days. Importantly, Mg doping not only made MIL-101(Cr, Mg) had higher surface area than MIL-101(Cr), but also created new and strong adsorptive sites for CO2 confirmed by TPD experiments. As a result, CO2 adsorption capacity of MIL-101(Cr, Mg) was significantly improved, and reached 3.28 mmol/g at 298 K and 1 bar, having an increase of 40% in comparison with MIL-101(Cr). More importantly, the CO2/N-2 adsorption selectivity of MIL-101(Cr, Mg) was significantly enhanced up to 86 at 100 kPa, being similar to 4 times of that of MIL-101(Cr). The strategy of doping metal ions can be an effective way to improve the adsorption performance of MOFs. (c) 2016 Elsevier Ltd. All rights reserved.