No gaseous guests have ever been discovered that can form sH clathrate hydrates. Herein, we show that a large molecular fluorinated gas (octafluorocyclobutane, c-C4F8), can stabilize the crystal structure of sH clathrate hydrate by occupying large (5(12)6(8)) cages. The inclusion of c-C4F8 molecules in sH clathrate hydrate in the presence of CH4 molecules was clearly demonstrated through three-phase (clathrate hydrate (H)-liquid water (LW) -vapor (V)) equilibria, powder X-ray diffraction (PXRD) and C-13 NMR spectroscopy. The discovery of a gaseous sH former, c-C4F8, contributes to broadening clathrate hydrate science and engineering by expanding target components for sH clathrate hydrates, and also offers excellent potential in various applications of sH clathrate hydrates, especially in clathrate hydrate-based gas separation.