Capturing CO2 from ambient air is known as a carbon-negative technology to reduce anthropogenic CO2 emissions in the air. Porous silica containing polyethyleneimine is one of the candidate sorbents for CO2 capture.[1] For enhanced adsorption capacity of CO2, amine-impregnated and -grafted porous silica have been considerably investigated. However, there are several drawbacks such as leaching of amine, complex process.[2,3] To overcome these kinds of weakness, we synthesized polyethyleneimine-silica nano-composites not impregnating and grafting but one-pot technique with directly incorporated amine. Our results show that polyethyleneimine was uniformly dispersed into the silica nanoparticles and its contents vary in a wide range. Also, the polyethyleneimine in the silica nanoparticles did not leach. By controlling reaction parameters, the morphology and size of silica nanoparticles can be variously tuned. These porous silica nano-composites including polyethyleneimine are a promising solid adsorbent for CO2 capture