||This study investigated the influence of CO2 injection into CH4 (90%) + C3H8 (10%) hydrates on structural transition and cage-filling characteristics for CH4 recovery and CO2 sequestration. The relationship between the replacement efficiency and the partial structure-transition was revealed using a powder X-ray diffraction. In addition, the quantitative analysis on the cage-filling characteristics in the multi-structural system after the replacement suggested the structural transition boundary depending on the occupancy of the guest molecules. The guest-exchange behavior from in-situ Raman study demonstrated that the rapid guest-exchange occurs first at the surface and thereby the initial sII hydrate is converted into the CO2-rich sI hydrate from the surface to its inner side. The overall results can offer the experimental evidence of the relationship between the replacement efficiency and the partial structure-transition in the replacement, and can provide further insights into the cage-specific occupation of external gas molecules for the replacement occurring in sII hydrates.