CO2 injection is considered as an alternative method for recovering shale gas and storing CO2 permanently into the geological trap. To better understand this field, an experimental study was carried out using shale samples from the Middle Magdalena Valley Basin in Colombia to investigate the adsorption mechanism of CO2 on shales. The effect of mineral composition, total organic carbon (TOC) content and thermal maturity on CO2 adsorption capacity has been discussed. The exper-iments were carried out using the manometric method to measure the excess sorption isotherms of CO2 at 50°C and pressures up to 3.5 MPa. The results indicate that the effect of clay minerals is not very significant in the adsorption of CO2; TOC has a major contribution to the adsorption uptake. In addition, a conclusive effect of maturity needs further measurements.