The large volume o Rui He f the using of Portland cement makes the industry a large emitter of CO2 despite it has a relatively low carbon footprint compared to most other construction materials. The CO2 curing has been found to be an effective method to achieve carbon neutrality of cementitious materials. In this work, cementitious materials with the addition of nano-silica were cured by CO2. The carbon footprint of cementitious materials with and without the addition of nano-silica was calculated. The mechanical performance of cementitious materials cured by CO2 is tested. The chemical composition of cementitious materials cured by CO2 incorporated with various dosage of nano-silica is characterized by thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). The pH value change of cementitious materials after CO2 curing is measured. The pore structure of cementitious materials is characterized by mercury intrusion porosimetry (MIP) and 3D X-ray microscopy (Micro-CT) techniques. The morphology of CO2 curing products is also characterized by scanning electron microscope (SEM) analysis. The results indicates that the CO2 curing method can significantly reduce the car-bon footprint of cementitious materials. The addition of nano-silica can improve the mechanical performance and result in a dense microstructure of cementitious materials.