The process of CO2 adsorption on silicalite-1 zeolite (MFI-type) is revealed using a single-crystal X-ray method. The structure of CO2-silicalite-1 with a small amount of CO2 in the pore is determined, wherein most of CO2 molecules are located in the straight channel. It indicates the straight channel is the most stable sorption site based on the van der Waals interactions between the CO2 and the framework, and the CO2 molecules initially adsorb in the straight channel in the adsorption process. This is the first report to describe the structure of MFI-type zeolites with the adsorbate molecules occupying only the straight channel.