||In this study, the phase equilibria of the CH4 + CO2 + methylcyclopentane (MCP) hydrates were compared with those without MCP to elucidate the influence of MCP on the thermodynamic hydrate stability for the replacement. Also, to identify the structure of CH4 + CO2 + MCP hydrates depending on the CO2 concentrations, and to examine the influence of replacement on the cage-specific guest distributions, the CH4 + CO2 + MCP hydrates and the replaced hydrate with CO2 were analyzed using 13C NMR spectroscopy. The hydrate phase behavior and 13C NMR spectroscopy results demonstrated that CO2 functions as a co-guest of sH hydrates in CH4-rich conditions and that the structural transition of sH to sI hydrates occurs in CO2-rich conditions. Through the molecular dynamics simulation, it was verified that the structural transition involved the dissociation of initial sH hydrates and subsequent reformation of sI hydrates. The overall experimental and computational evidence can provide further insights into the exchange behavior of the guest molecules for the replacement mechanism occurring in sH natural gas hydrates.