Biogas mixtures include methane (which is useful), carbon dioxide, and hydrogen sulfide (which can be a nuisance). To remove hydrogen sulfide from biogas, we conducted separation experiments using tetra-n-butyl ammonium bromide semi-clathrate hydrate (hereafter referenced as TBAB hydrate). TBAB hydrate is stable under atmospheric pressure and can cage gas molecules in their empty small cage. A solution of 10 wt % TBAB was enclosed in a pressure vessel with a gas mixture containing hydrogen sulfide, and then TBAB hydrate was formed in the solution by cooling. Because of the selective incorporation of hydrogen sulfide into TBAB hydrate, > 90% of the hydrogen sulfide in the vapor phase was removed during the hydrate growth. We also determined that the removal efficiency of hydrogen sulfide was not dependent on the initial pressure or the cooling rate. The results showed that TBAB hydrate was an effective material for desulfurization.