This paper reports the identification of the crystallographic structure of the clathrate hydrate formed in a system of methane + propan-1-ol + water. A hydrate crystal sample was prepared with a 0.0556 mole fraction aqueous solution of propan-1-ol pressurized with methane and then subjected to powder X-ray diffraction and Raman spectroscopic measurements. The X-ray diffraction pattern thus obtained from the sample indicated that the crystallographic structure of the hydrate was structure II. The Raman spectra thus obtained from the same sample indicated that the methane molecules occupied not only 5 12 cages but also 5(12)6(4) cages.