In this study, nanofluids of nanosilica and carbon nanotube have been applied as absorbents in a gas–liquid hollow fiber membrane contactor for CO₂ separation. A gas mixture of air and CO₂ was fed into the shell side in contact with pure water or nanofluid which was fed into the fibers. Effects of different parameters including the type of nanofluid, nanoparticle concentration, liquid and gas flow rates, liquid temperature and CO₂ inlet concentration were investigated experimentally on the removal efficiency of CO₂. The results showed that the injection of 0.5wt% silica nanofluid increased the removal efficiency up to 20% at low liquid flow rates (compared to distilled water) while the increase is about 9% at high rates. Nanofluid of carbon nanotube showed much better separation than the silica and it enhanced the removal efficiency up to 40% and 20% at low and high liquid rates respectively. The CO₂ removal efficiency of pure water and silica nanofluids slightly decreased with increasing CO₂ inlet concentration which is possibly due to the saturation of these fluids. However the removal efficiency of carbon nanotube was nearly constant and even enhanced in some flow rates with increasing CO₂ inlet concentration.