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Laboratory experiments were performed to measure the supercritical CO2 (scCO2) storage ratio (%) of conglomerate and sandstone in the Janggi Basin, which are classified as rock in Korea that are available for CO2 storage. The scCO2 storage capacity was evaluated by direct measurement of the amount of scCO2 replacing the pore water in each reservoir rock core. The scCO2 sealing capacity of the cap rock (i.e., tuff and mudstone) was also compared by measuring the scCO2 capillary entry pressure (Δp) into the rock core. The measured average scCO2 storage ratio of the conglomerate and the sandstone were 30.7% and 13.1%, respectively, suggesting that the scCO2 storage capacity was greater than 360,000 metric tons. The scCO2 capillary entry pressure for the tuff ranged from 15 to 20 bar and for the mudstone it was higher than 150 bar, suggesting that the mudstone layers had enough sealing capacity from the aspect of hydromechanics. From XRF analyses, before and after 90 d of the scCO2-water-cap rock reaction, the mudstone and the tuff were investigated to assure their geochemical stability as the cap rock. From the study, the Janggi Basin was considered an optimal CO2 storage site based on both its high scCO2 storage ratio and high capillary entry pressure. [ABSTRACT FROM AUTHOR]