In this work, suspensions of Fe 3 O 4 , CNT, SiO 2 , and Al 2 O 3 nanoparticles in distilled water are produced and tested as new absorbents in a gas−liquid hollow fiber membrane contactor to investigate the effect of nanoparticles on the rate of mass transfer during CO 2 absorption. For this purpose, a pilot-scaled hollow fiber membrane contactor was constructed. A gas mixture was passed through the shell-side, and the nanofluid flowed cocurrently through the lumen side of the fibers. The effects of different operating conditions including gas flow rate, liquid flow rate, inlet CO 2 concentration, and nanoparticle concentration on the CO 2 absorption have been studied. The results showed that among the operating parameters, liquid flow rate and nanoparticle concentration had the greatest effects on the CO 2 absorption. Moreover, UV−vis spectroscopy and DLS method were employed to explore the dispersion stability and hydrodynamic diameter of nanoparticles in the base fluid. The results revealed that nanofluid stability and hydrodynamic diameter of nanoparticles in the base fluid are the key factors in nanoparticle selection for CO 2 absorption in membrane contactor. The obtained results showed that the highest absorption rate enhancements for nanofluids are 43.8% at 0.15 wt % Fe 3 O 4 , 38.0% at 0.1 wt % CNT, 25.9% at 0.05 wt % SiO 2 , and 3.0% at 0.05 wt % Al 2 O 3 , as compared to the absorption rate by base fluid.